IREGON RULE CO. 1 U.S.A. 2 






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AN ELEMENTARY TREATISE 



SENSE-PERCEPTION 



■ S 



\0* ' \ Julian Munson Sturtevant 

Ex-President of Illinois College 



*& 



NEW HAVEN : 

T U T T L E , MOREHOUSE & TAYLOR, PRO T IS R S , 
1863. 



} 












NOTE 



This little treatise is printed for the benefit of the classes under 
my instruction, not published. I have, however, taken the liberty 
of sending copies of it to a few teachers and particular friends, 
whose judgment of it I am very desirous of obtaining-, because I 
have tbe greatest respect for their opinions of such a matter. An 
expression .of their judgment addressed to me at Jacksonville. 
Illinois, will be very gratefully received. 

J. M. BTUETEVANT. 

WARREN, Conn.. July 26th, 1883. 



Copyright, 1883, by J. M. Sturtevani 




SENSE-PERCEPTION. 



CHAPTER I. 



Preliminary. 



§ 1. It is unnecessary at the beginning of this Trea- 
tise, to say more of the nature of the human soul than 
that every man consciously. possesses the power to know, 
to feel and to choose. The human soul is that entity to 
which these powers belong. The existence of these 
powers and of this entity admits of no question. If we 
cannot know this, we cannot know anything. Inquiry 
is meaningless and science impossible. 

It is equally unquestionable, that, at the beginning of 
human life, we are in the profoundest ignorance of 
everything. It will also appear more and more in the 
progress of this Treatise, that all knowledge is acquired 
through the activities of a rational soul, exerting its own 
powers through the bodily organism with which it is 
connected. It is the design of the Treatise now under- 
taken to point out the conditions under which and the 
processes by which the soul so exerts these activities, as 
to find its way out of the ignorance in which it begins 
to be, into a clear knowledge of itself and of the mate- 
1 



2 SENSE-PERCEPTION. 

rial universe. Itself it must know, as a condition of 
knowing anything else ; for the beginning of all knowl- 
edge is self-knowledge. "Know thyself" is not only a 
rule of wisdom, but of necessity. 

§ 2. In the construction of a Treatise on any science, 
the meaning of certain words must be assumed without 
any definition. The knowledge of their meaning can- 
not be communicated from one mind to another by a 
definition, but must spring up in each mind through its 
own experience independently of the action of any other 
mind. If there is not in any mind such an independent 
experience, the meaning of the word which expresses 
that experience can in no manner be known. Many 
minds all having the same idea derived from experience, 
or occasioned by it, can agree together upon a word by 
which that idea shall be expressed. 

Such a word is " knowledge." Its meaning can only 
be understood by an experience of knowing. In the 
progress of this Treatise, we must often employ words 
of which the same is true. All men use such words, 
not only in science, but in all human intercourse. The 
use of such words always assumes and implies the inde- 
pendent mental activity both of him who employs them 
and of those to whom they are addressed. Human inter- 
course itself thus assumes the individual personality of 
all human beings, that is, that every individual possesses 
or rather is a rational soul. 

We can make no progress in the inquiries upon which 
we are entering without assuming the fundamental facts 
of human consciousness. It is therefore necessary to de- 
fine that word. 

Definition.— Consciousness is the knowledge or the 
power of knowing one's own mental states and activi- 
ties. 



SENSE-PERCEPTION. 3 

In consciousness therefore all knowledge begins. It 
is in consciousness, the conscious experience of joy or 
sorrow, of desire, gratification or purpose, that the fact 
of our own existence is originally revealed to us. It is 
by the experiences of which we are conscious, that all 
those activities are excited and stimulated by which 
knowledge is acquired and a human life rendered possi- 
ble. It is unnecessary to our present purpose to enter 
into any of those inquiries respecting the nature of con- 
sciousness which have attracted the attention of the 
curious. It is quite enough to recognize the fact that 
the human soul has the power of knowing its own 
thoughts, its own experiences of pain or pleasure, its own 
activities and purposes. This power we call conscious- 
ness. 

§ 3. It is necessary in this place to say a few words 
respecting those bodily organs which are the instru- 
ments employed by the soul in the various processes of 
sense-perception. Every portion of the bodily organism 
is, in greater or less degree, subsidiary to these processes. 
It is, however, important to our purpose, to call special 
attention to three distinct systems of the bodily organ- 
ism, — the muscles, the nerves, and the special senses. 
All these sustain an intimate relation to our subject. 

The muscles are those parts of the bodily organism by 
the contraction and relaxation of which all the motions 
of the body are produced. Without them we shall see 
as we proceed, the whole arrangement of nerves and 
special senses would be powerless to convey to the mind 
any knowledge of the material universe. This fact it is 
important to our purpose distinctly to recognize. Be- 
yond this it is unnecessary to go further in the examina- 
tion of the muscular system. For such an examination 
the student must be referred to the anatomists. 



4 SENSE-PERCEPTION. 

Important as the nervous system confessedly is to our 
subject, it is unnecessary for us to enter upon its exami- 
nation, more than simply to recognize two of its func- 
tions. Those functions are voluntary motion and sensi- 
bility. To each of these functions certain nerves are 
distinctly appropriated. Every muscle of the body is 
furnished with its own appropriate nerve through which 
it communicates with the brain, and without the health- 
ful action of which the power of the muscle cannot be 
exerted. Some of these nerves are called into action 
only by the will, and always obey its behests. These 
are the nerves of voluntary motion. Other nerves act 
spontaneously, without the action of the will, and main- 
tain in perpetuity the vital movements of the heart, the 
lungs and other vital organs. These are nerves of in- 
voluntary and spontaneous motion. They begin to act 
with the very beginning of life and cease their activity 
only at death. 

§ 4. The other function of the nervous system is that 
of sensibility or feeling. The nerves which are appro- 
priate to this function originate, like those already de- 
scribed, in the brain, and are distributed, in greater or 
less degree, to every portion or tissue of the living 
organism. On the presence of these nerves, the sensi- 
bility of the whole body depends. Their function is 
twofold, general sensibility and special sensation. The 
former of these functions is present in every portion of 
the body with the exception of the hair and finger and 
toe nails. It is found even in the hardest bones. At 
this point the two functions of general sensibility and 
motion are very intimately united. To every muscle of 
the body, a nerve of sensibility and a nerve of motion 
are conveyed enclosed in the same sheath. Along the 
one any sensation experienced is reported at the nervous 



SENSE-PERCEPTION. 5 

center, to which the nerve of motion spontaneously re- 
sponds by exciting such muscular action as the exigency 
requires. Thus if the light admitted to the eye is pain- 
ful to the optic nerve, a reflex muscular action takes 
place, by which the pupil is contracted, so as to admit 
less light to the eye. A similar relation between nerves 
of sensibility and nerves of motion pervades the living 
organism. Motion so produced must however be sharply 
distinguished from voluntary motion. The latter is 
very intimately, the former not at all, related to sense- 
perception. 

§ 5. The nervous system, as the source of the sensi- 
bility of the living organism, must be viewed in a three- 
fold aspect. 

1. The general sensibility. This, as already stated, 
pervades the whole living organism. It responds to the 
slightest touch of the surface of the body by any ma- 
terial substance, to the change of temperature of any 
portion of the body whether internal or superficial, and 
to all irritations or lesions from whatever causes origi- 
nated. It is connected in greater or less degree with 
the spontaneous action of all the vital organs. When, 
however, the vital organs are in normal condition, and 
their functions are healthfully performed, their action is 
attended by little or no sensibility. A man in perfect 
health scarcely knows that he has a bodily organization. 
But when they are deranged by disease, their action is 
often attended with most distressing and painful sensi- 
bility. 

2. Another aspect in which the nervous system as 
related to sensibility must be viewed is, the muscular 
sensibility. In this aspect of it, we find the first step 
which the mind takes towards a knowledge of the ex- 
ternal universe. The action of every voluntary muscle 



6 SENSE-PERCEPTION. 

of the body is attended by its own peculiar sensibility. 
It is by the experience of that sensibility, that the soul 
learns what muscle must be brought into action to pro- 
duce any given motion, and what muscle is in action 
when a given motion is produced. It is by observing 
the sensibility of each muscle that the soul acquires the 
power of voluntary motion. The almost incessant mo- 
tions of the limbs of a new-born infant are neither 
guided by the intelligence nor controlled by the will. 
The first problem which the rational soul has to solve is? 
to gain the control of the motions of the body and the 
limbs. It is only by the muscular sensibility that the 
solution of this problem is rendered possible. We shall 
learn as we proceed that it is here that the soul acquires 
its first idea of an extended and external universe. 

3. The remaining aspect in which the nervous system 
is to be viewed, has reference to the action of the special 
senses. These are commonly said to be five in number, 
viz : touch, sight, hearing, taste, smell. From this state- 
ment it seems necessary to dissent. What is called 
touch cannot with propriety be regarded as one of the 
special senses. The reasons for this dissent, however, 
cannot be fully stated in this place, but will be ren- 
dered apparent as we proceed. One reason however is 
here apparent. The special senses have each a special 
organ, by which only the function of the sense can be 
performed. Touch has no such organ, but is found in 
greater or less degree in all parts of the surface of the 
living body. This alone is a full justification for class- 
ifying it as a part of the general sensibility and not as 
a special sense. 

We cannot, however, regard this enumeration of the 
special senses as exhaustive. Sex appears to be entitled 
to be ranked with the special senses. It however per- 



SENSE-PERCEPTION. 7 

forms so small a function in the soul's knowledge of the 
external universe, that a consideration of the indelicacy 
of the subject seems to justify its omission in a treatise 
on sense-perception. Its function is very closely analo- 
gous to that of taste, sustaining the same relation to 
the perpetuation of the species that taste does to the 
life and health of the individual. 



CHAPTER II. 



Three Fundamental Questions Considered. 

§ 6. Every student of the human mind must neces- 
sarily meet, almost at the outset of his enquiries, three 
questions, which underlie the whole subject. 

I. What is the origin of the idea of duration ? 

II. How does the mind acquire the idea of an ex- 
tended surface or body ? 

III. How does the mind acquire the idea of exter- 
nality or outness ? 

I. These questions are to be considered in the order 
in which they have been propounded. We here encoun- 
ter one of the words which admit of no definition. He 
who has not derived from his own mental activities 
and experiences the idea expressed by the word dura- 
tion can never get that idea from a definition. Two 
persons both of whom have it may agree upon the name 
by which it shall be called ; but we must account for its 
origin in every mind by its own independent action. 



8 SENSE-PERCEPTION. 

The soul knows itself to exist as a permanent entity 
by its experiences of pleasure or pain, activity or rest.* 
From the beginning of our existence these experiences 
occur in almost unceasing succession. We now expe- 
rience pleasure, next we suffer pain, next we are active, 
next we have ceased to act and are at rest. We know 
these changes as successive one to the other. One 
goes before, another follows after. This necessarily 
gives the idea of duration, now and then, longer and 
shorter. Since one event, many soul experiences have 
occurred, since another, very few. Thus every being 
that exists and is capable of knowledge, and is con- 
scious of existing in a succession of mental states, must 
know events as involving duration. If a soul could 
exist having no knowledge of things external, but only 
of himself, that soul would not lack the idea of dura- 
tion. He would know himself as existing in a perpet- 
ual succession of changes. 

§ 1. II. How then originates the idea of extension ?f 
This word is also incapable of definition. It stands in 
this respect on precisely the same footing as duration. 
We all have the idea which the word expresses, and can- 
not divest ourselves of it. We conceive of all bodies 
as having length, breadth and thickness. But like dura- 
tion this idea has come to us not by any definition, but 
by the activity of our own minds. How then does this 
idea arise in the mind by occasion of the experiences 
to which it has been subjected ? 

It is obvious that this question is far more complicated 
than the question of the origin of duration. That in- 
volves nothing but a succession of soul-experiences ; 
but this involves the soul's use and control of the bodily 

* "Reid's Collected Writings, pp. 342, 343. 

fReid's Collected Writings, pp. 123-126. 142-144, 528. 



SENSE-PERCEPTION. 9 

organism. It is only through the organs of the body, 
that the mind deals with material things. 

It seems to me that few persons will be disposed to 
deny the proposition, that if the body and all its organs 
were incapable of motion, the mind could never so 
mal^e use of the senses as to acquire the notion of ex- 
tension. To a soul so limited in its powers, there could 
be no here and no there, as there could be no now and 
no then to a soul that experiences no changes. 

We have yet made but little progress in our task; 
yet by this assertion we are brought into direct conflict 
with writers of the highest authority. This assertion 
however we shall endeavor fully to substantiate as we 
proceed. It must here be taken, not as a proposition 
which we claim to have proved, but as one which we 
expect to establish.* 

In our judgment, the only answer which can be given 
to the question, what the origin of the idea of exten- 
sion is, that it springs up of necessity with the earliest 
exercise of the soul's power of controlling the motions 
of the body. How different the development of the 
human infant, from that of the young of brute animals ! 
The latter are for the most part able to control their 
limbs, and to use them for their own help and preserva- 
tion, from the moment of birth, and must depend upon 
them or perish, and where this is not true of all their 
bodily organs, as in the case of the young bird in the 
nest, it is still true of certain organs. The young bird 
must stretch up its neck and open wide its mouth, to 
receive the food which the parent bird drops into it, or 
it will starve to death. In the case of the human in- 
fant, the source of its food must be placed within its 
lips, and the action of obtaining its food is as sponta- 

* Porter's Elements, Sec. 83. 
2 



10 SENSE-PERCEPTION. 

neous and unintelligent as the beating of its heart. At 
this point, human and brutal life are on the same level. 
Beyond this the infant's preservation and well-being must 
depend alone on intelligence. Over the motions of its 
limbs and head the new-born infant has no control. It 
is utterly helpless, and must perish very speedily unless 
its wants are supplied by the intervention of an intelli- 
gence not its own. 

From this condition of utter helplessness, the human 
infant can only escape by learning, in the use of its own 
rational powers, to control and guide the motions of the 
limbs and organs of the body. The hands and feet of 
an infant are often in motion ; but those motions are at 
first controlled by no intelligence or will power. They 
are aimless, and useless for the supply of the wants of 
the child. The first lesson of infancy is to learn to con- 
trol and guide these motions ; and in the process by 
which this acquisition is made, the idea of extension 
begins to manifest itself. The notion of place, here and 
there, is necessarily suggested by all motion voluntarily 
and consciously begun, continued and terminated. The 
child voluntarily moves his own hand. The beginning 
of that motion is here, the end of it is there, and the 
continuance of it suggests the extension that separates 
them. The distinction between the ego and the non-ego 
may not yet have been thought of; but the position of 
that something which I voluntarily move must be recog- 
nized as changed, here and there must be distinguished, 
and the intervening distance. This is the idea of exten- 
sion in its most rudimentary form, and it must spring up 
in the mind with the first exercise of the power of volun- 
tary motion. The child that has learned intentionally to 
move his hand, or to open and shut it, or to turn his 
eyes from side to side, or to turn his head on the joint 



SENSE-PERCEPTION. 11 

of his neck, must have learned the distinction between 
here and there, and that distance separates them. 

It is not claimed that this is the fully developed idea 
of extension in its three dimensions, or even of an ex- 
tended surface. In order to acquire the full conception 
of an extended surface, the notion of body must have 
been gained, and the ego must have been distinguished 
from the non-ego. 

§ 8. III. Our next inquiry is, how is this acquisition 
made ? Perhaps the gravest difficulty we must encoun- 
ter in our enquiries into the genesis of human knowledge 
is here. How does the soul pass from the knowledge of 
itself to the knowledge of that outer universe which is 
not itself ? 

Before, however, proceeding to answer this question, it 
seems necessary to define two terms which we can hardly 
avoid using in the discussion. They are the two cor- 
relative terms "subjective" and "objective." In using 
these two terms, we regard them as an exhaustive divis- 
ion of all the knowable. All the objects in the universe 
are comprehended either in myself or in the universe 
outside of myself. All then which I know of myself, 
my own thoughts, feelings, joys, sorrows, acts, intentions, 
is subjective knowledge. All which I know of the uni- 
verse outside of myself is objective knowledge. 

At the threshold of this inquiry we meet the stubborn, 
indisputable fact, that at the beginning of the soul's ac- 
tivity, all its knowledge is purely subjective. It is true 
from the very first, that most of our experiences are 
caused by impressions which the universe outside of our- 
selves makes upon us. But these impressions are purely 
subjective.* The new-born infant knows nothing of the 
causes which produce them. For example, a loud noise 

* Porter's Elements, Sec. 83. 



12 SENSE-PERCEPTION. 

is made near an infant's ear. He experiences the sensa- 
tion, and is startled and distressed by it ; but he knows 
nothing of its cause. It is to him only a subjective feel- 
ing, and suggests no idea of anything external to him- 
self. The same is true of all the impressions which are 
made upon him through any of his senses. All the im- 
pressions which are made upon the inexperienced infant, 
through the eye, the ear, the taste, the smell, are mere 
subjective sensations. This statement will be called in 
question by some and will be more fully discussed fur- 
ther on. 

We shall however at this point sufficiently anticipate 
the subsequent discussion to illustrate it by a single ex- 
ample. Let us suppose that a man of good natural un- 
derstanding had been, up to a certain time of his mature 
life, quite destitute of the sense of smell, and had never 
been informed that other people had such a sense. At 
last, while he is quite alone in his room, he is suddenly 
endowed with that sense in full acuteness. At the same 
moment his room happens to be filled with some intense 
and disgusting odor, say of assafcetida ; I affirm that the 
new sensation would be purely subjective, and he would 
probably think himself attacked with disease, and per- 
haps hastily call a physician. Sitting still in his chair, 
the offending substance probably being in some remote 
part of the room, he would not even have the power of 
referring the new sensation to that part of the nostril 
where the nerve of smell is situated. We do not make 
such a reference of a sensation of smell to that nerve, 
even after years of experience. We have learned indeed 
that the nostril is the place of the sensation, by finding 
that the odorous object must be applied to the nostril 
in order that the sensation may be most intense ; but 
we do not know, till we have studied the matter ana- 



SENSE-PERCEPTION. 13 

tomically, in what particular part of the nostril that 
nerve is situated, or how extensively the nostril is per- 
vaded by it. In such a case as we have supposed, the 
man would have no power of locating the sensation in 
the nostril even. The same will hereafter be proved to 
be true of all the special sensations. They are all sub- 
jective experiences, which the soul has no original 
power of referring either to their external causes, or to 
the part of the body where they are produced. 

§ 9. Our question then is narrowed down to a point : 
how does the soul acquire the power of referring the 
impressions that are made upon it by the outside uni- 
verse to the causes by which they are produced ? How 
does it pass from the knowledge of subjective impres- 
sion to a knowledge of objective causation ? One thing 
must here be conceded by all. By the mere experience 
of subjective sensation, the mind never can acquire a 
knowledge of an external objective cause. For exam- 
ple, a hard substance touches the surface of one's body. 
It is purely a subjective sensation, and no repetition of it 
can give any more idea of the objective cause than the 
first experience of it. 

We shall find no answer to our question till we go 
back to the same cause which conducted us to the first 
idea of extension. Here we shall find the solution. Let 
us suppose that the infant had at last subjected his mus- 
cles and the limbs which those muscles move, to the con- 
trol of his intelligence and his will. He is perfectly con- 
scious of a power to move his hand in any direction at 
pleasure. But on a certain occasion, he finds a motion 
of the hand which he is perfectly conscious of being able 
to make, resisted and effectually stopped. Here then is 
the ego conscious of power to do a given thing, stand- 
ing face to face with a resisting non-ego, that is, a power 
3 



14 SENSE-PERCEPTION. 

resisting and hindering his own power in action. Nor 
let us suppose that the infant mind stops here. It is 
true that it is chiefly employed in the problems of sense- 
perception ; but all the faculties cooperate from the first. 
We shall show further on, and in doing so be sustained 
by the highest authority, that infancy does use induc- 
tive reasoning* in the solution of some of the simplest 
problems of sense-perception. It is just as reasonable 
to believe that it employs in like cases the intuition of 
cause and effect as -the law of induction. What diffi- 
culty then in admitting that in resistance experienced it 
sees a resisting cause? Indeed the whole problem of 
sense-perception necessarily involves the notion of caus- 
ation. To perceive is to refer our sensations to their 
appropriate causes. If the infant has not the power of 
passing from a known effect to a knowledge of its cause, 
it has no power of sense-perception, for this is sense-per- 
ception. He does not infer an objective cause from a 
subjective sensation, but the existence of a resisting 
agent from an experience of his own activity resisted. 

President Porter claims that the non-ego which is 
known in sense-perception is " the bodily organism itself 
or that part of the sensorium which is excited to action." 
To this it may be replied, that in the proper place it has 
been abundantly shown, that in many cases of sense- 
perception, if not indeed in most cases, we never do 
refer the sensation to the part of the organism in which 
it is produced. We see perfectly without referring the 
sensation of vision to the retina of the eye, or knowing 
that we have any retina. The same thing holds in re- 
spect to all the senses. The non-ego which is discerned 
is not our own organism but that which resists our will 
power. It is by such resistance alone that we learn the 
existence of the non-ego.f 

* Porter's Elements, Sec. 109. f Porter's Elements, Sec. 86. 



SENSE-PERCEPTION. 15 

It is important to be noticed, that in acquiring such a 
notion of a resisting non-ego, the mind does not neces- 
sarily employ the aid of either of the special senses. In 
the act of voluntary motion and in the cognition of the 
resistance experienced to it, the mind employs only its 
muscular power and muscular sensibility. Even in 
recognizing the existence of a resisting power, the mind 
does not necessarily call into exercise what is commonly 
called the sense of touch. The muscular sensibility 
alone conveys to the mind the consciousness of the act 
of voluntary motion and the experience of its resistance 
and arrest. 

§ 10. This notion of externality is only rudimentary, 
sustaining nearly the same relation to the fully devel- 
oped idea that the notion of extension which is implied 
in all voluntary motion, does to the completed concep- 
tion of an extended surface. Perhaps, however, it will 
not be found difficult at this point of the discussion, to 
indicate the manner in which the development of both 
these ideas is completed. At this stage of the process, 
the mind will soon perceive that this resistance is expe- 
rienced only within certain boundaries. Nothing hin- 
ders but that these boundaries should be definitely ascer- 
tained, and ascertained on all sides. In this process the 
mind has become master of all the conditions of the full 
development of the idea of a straight line and of a resist- 
ing extended surface. With this latter also the idea of 
hardness is inseparably linked. Indeed the two ideas 
are identical. 

This, however, only accounts for the origin of the 
idea of extension in the two dimensions of length and 
breadth. The question still remains, how does the mind 
pass to the third dimension of space, or to the knowl- 
edge of solid bodies ? In order to answer this question, 



16 SENSE-PERCEPTION. 

it is not necessary to introduce into the discussion any- 
other factor than voluntary motion and muscular sensi- 
bility. The mind is capable of cognizing the fact of a 
change of direction in that motion, and of continued 
resistance in that changed direction, when the resistance 
is interrupted in a straight line. This is sufficient to 
reveal two resisting surfaces standing at an angle to 
each other. This process is capable of being extended 
to all the plane surfaces by which a solid body is 
bounded. In a similar manner the lines in which the 
several planes bounding a body meet may be traced, its 
solid angles may be discovered and a conception of its 
outline completed. In tracing the bounding lines of the 
several planes, the general sensibility to contact will 
render important aid. It is also easy to see, that when 
the dimensions of the body are not greater than can be 
grasped by one hand or by the two hands, the muscular 
power of one hand may be exerted in the direction oppo- 
site to that of the other, and thus it will become obvious 
to the mind that the body has two surfaces separated 
from each other by its third dimension. In no part of 
the process does the mind require any other aid than 
voluntary motion and muscular sensibility. 

In all these processes doubtless the action of what is 
commonly called the sense of touch and the sense of 
sight, will be present and consciously active, but their 
activity will not be necessary to the processes we have 
been describing. It will, however, be readily admitted 
that the general sensibility of the surface of the body 
greatly facilitates the process by which we pass from a 
knowledge of the extended surface to that of the solid 
body ; yet it cannot be admitted that it is indispensable. 

§ 11. It does not fall in with the plan of this treatise 
to enter upon any extended discussion of the intuitive 



SENSE-PERCEPTION. 17 

faculty of the soul ; but it is necessary at this point to 
assume the existence of such a faculty, and its activity 
in these earliest processes of the mind. A rational soul 
cannot act in such a manner as to acquire knowledge, 
without recognizing the relation of cause and effect. It 
may be objected to the foregoing argument, that in 
these earliest processes of the infant mind, it has as yet 
no notion of this relation. But why not ? It is a con- 
dition of the very first step toward any knowledge of 
the external, that the soul should know itself as a cause, 
that it should be conscious of power in action. It is in 
this very consciousness, that the notion of cause and 
effect originates in the soul. He that knows himself as 
a doer, knows a cause, knows the thing done as an effect, 
and is fully prepared to know that which resists his 
causative power as another cause distinguished from and 
set over against the cause which is resisted. This con- 
clusion cannot be set aside otherwise than by denying 
that the infant has a rational soul, and to deny this is to 
deny that it has any power of acquiring knowledge. 



CHAPTER III. 



The Special Senses. 

§ 12. In the incipient processes thus far described, the 
soul has laid for itself a substantial foundation upon 
which the whole superstructure of its knowledge of the 
material world is to be built. It now remains to exam- 
ine those processes by which the soul in the use of the 



1 8 SENSE-PERCEPTION. 

special senses constructs and rears up that superstruc- 
ture. As preparatory to this examination, it is neces- 
sary to call the attention of the student to two words, 
the use of which we have as far as possible avoided. 
They are "sensation" and "perception."* These words 
are used in popular speech in a wide diversity of import, 
and so must they continue to be used. Sensation is not 
only used to express all those feelings which we are 
liable to experience in consequence of change of bodily 
condition, but even the mental emotions whichare in no 
way caused by any affection of the body. We call the 
coldness which we experience on laying the hand on a 
piece of marble, or a pain in the head or hand, or the 
excitement which an eloquent orator produces on his 
audience, a sensation. In like manner we speak of per- 
ceiving the force of an argument, or the point of a witti- 
cism, or the truth of a proposition, or the beauty of a 
landscape. In popular discourse, there is no objection 
to this ; but in order that these words may do service as 
the technical terms of a science, they must be limited to 
a precise and exact meaning. The following definitions 
are proposed :f 

Definition. — Sensation is the impression made on the 
mind by the action of an appropriate external object on 
the organ of some one of the special senses. 

Definition. — Perception is the reference of a sensation 
to the external object by which the sensation was pro- 
duced, by which reference the mind comes to know that 
external object as having a causal power to produce 
that sensation. 

§ 13. It seems necessary to render our conception of 
the relation of these two factors in sense-perception to 

* Porter's Elements, Sec. 83, 85-87. 

f Reid's Collected Writings, p. 182. Porter's Elements, Sec. 81-87 . 



SENSE-PERCEPTION. 19 

each other and to the whole process, as precise and clear 
as possible. It is asserted by some that though these 
two stages in the process are distinguishable in thought, 
neither can ever exist without the other, that there can 
neither be any perception without sensation, or any sen- 
sation without perception.* To us it seems obvious 
that while there certainly can be no perception without 
sensation, there can and must be, especially in the first 
experiences of infancy, many sensations without any 
corresponding perceptions. Does the infant in the first 
hour after its birth experience no change of sensation, 
when the gas is extinguished, and total darkness follows 
bright illumination ? Must there not be a sensation of 
light, though he has not yet learned to interpret that 
sensation into a discernment of objects or surfaces, or of 
his eyes, as the place of his sensation ? Must not an 
infant of good hearing have the sensation of sound, 
while he is yet entirely unable to refer it to any external 
cause, or to distinguish it from a purely subjective feel- 
ing ? The case is too obvious to require further eluci- 
dation. The natural order of things is, that the infant 
first experiences a sensation, and then by the exercise of 
his active powers and his rationality interprets it, by 
referring it to its proper external cause. 

§ 14. It is also maintained that the mind always refers 
the sensation to the organ of sense in which it is pro- 
duced. This cannot be admitted. There are many sen- 
sations which even in mature life we do not so refer, till 
we are instructed to do so by the accurate observations 
of anatomical science. We do indeed learn by experi- 
ence while very young, that the ear is the organ of 
hearing; but we never learn to locate the sensation in 

* Hamilton's Metaphysics, p. 320, Bowen's edition. Porter's Ele- 
ments, Sec. 80. 



20 SENSE-PERCEPTION. 

the acoustic nerve, situated in the inner chamber of the 
ear, where only it originates, till science has taught us 
to do so by its accurate observations. No one ever does 
refer the visual sensation to the retina, lining the interior 
chamber of the eye, till science has taught him that that 
is the place of its origin, and even then we never acquire 
the consciousness that such is the fact. It is evident 
that the soul has no original power of referring visual 
sensations to the retina as their source. No one knows 
that sensations of smell originate in the interior of the 
nostril, or ever learns the situation or extent of that 
organ in the nostril till science has taught him. No 
man knows till he learns by experiment or by instruction 
from others, the limits of the sense of taste in his own 
mouth. The assertion that the mind at once refers its 
sensations to their proper place in the organism, and 
that even in infancy, is destitute of any foundation in 
truth. It is even contradictory to known fact. 

§ 15. It has been claimed that in intensity, sensation 
and perception bear to each other an inverse ratio, that 
is, that the more intense the sensation the less accurate 
and discriminating is the perception.* The facts ad- 
duced to substantiate this claim are such as these : that 
if the light is too intense, for example, if one looks di- 
rectly at the sun shining in its strength, the eye is daz- 
zled and no distinct vision takes place, or when the 
surface of the body is pressed or crushed with a certain 
degree of violence, or when the touching body is so hot 
or so cold as to be painful, there is no perception. There 
is a confusion of thought in the language in which some 
of these examples are expressed, which will require at- 
tention in another place. It is enough to say here, that 

* Hamilton's Metaphysics, page 320, Bowen's edition. Porter's 
Elements, Sec. 89. 



SENSE-PERCEPTION. 21 

these are all cases in which there is an actual injury- 
inflicted on the organ. The light may be so intense as 
to destroy the optic nerve, or at least temporarily to 
paralyze it. So also the contact may be such and under 
such conditions as to injure or disorganize the surface 
to which it is applied. It must also be borne in mind, 
that the sensibility which is excited by temperature is 
by no means entitled to be classed with special sensa- 
tions. Notwithstanding these facts, it is none the less 
true that, up to the point at which the light begins to 
be painful and disorganizing, it strictly holds, that the 
more intense the sensation the clearer and more dis- 
criminating the perception. If you wish to discern the 
finest possible black line drawn on white paper, you 
must place it in the intensest light which the organ can 
bear without injury. 

Authors have fallen into this error by failing to notice 
that, for the most part, the sensations have a double 
function. One of these functions is to furnish the mind 
with the necessary data of perception. The other func- 
tion is to impart to the soul a high and peculiar delight. 
Both these functions pertain in greater or less degree to 
the sensations furnished by each of the senses, though 
in very different degrees. It will be shown, as we pro- 
ceed, that in addition to the practical uses of the special 
sensations, they are made to minister in a high degree 
to the pleasures of life, and even to the most dignified 
and elegant culture of the intellect. The esthetic nature 
of man has for the most part its source in the sensations 
of the eye and the ear. 

§ 16. It has already been incidentally remarked, that 
each of the senses has its own peculiar organ through 
which alone the sensation appropriate to the sense can 
be experienced. If that organ is destroyed or rendered 

4 



22 SENSE-PERCEPTION. 

inactive, no other part of the body can yield the sensa- 
tion. If the organ has been permanently destroyed, the 
soul must remain destitute of the sensation. From this 
sensation, in the case of each of the special senses, is 
furnished to the soul a peculiar and original idea, which 
can be derived only from that sense, so that if that sense 
is wanting, the soul remains utterly destitute of the 
peculiar idea which is appropriate to it. 

It has already been remarked that what is commonly 
called the sense of touch has no such special organ. To 
this it must be added, that neither does it furnish the 
soul with any peculiar idea for the acquisition of which 
the soul is entirely dependent on that sense. If it is the 
source of any such peculiar idea, what is that idea? 
Temperature is often spoken of as an idea acquired by 
the sense of touch. But this cannot be so. The feeling 
of heat or coldness is not confined to the surface of the 
body, as touch is, if there is any such sense. It is capa- 
ble of being experienced in any part of the interior of 
the body as well as on the surface. It clearly belongs, 
not to the special sensations, but to what has already 
been defined as general sensibility. None of the pains 
of the body, whether resulting from disease or lesion, are 
to be ranked with the special sensations. 

The idea of outness cannot, as has been already shown, 
be furnished by contact. That is a mere subjective 
feeling until it is interpreted to the mind through volun. 
tary motion and the experience of resistance. It should 
be mentioned that the mind derives important assistance 
in distinguishing the parts of its own body from other 
material bodies touched or handled, from the fact, that 
when we touch parts of our own bodies, the feeling is 
experienced both in that which touches and that which 
is touched ; while on the other hand when we touch some 



SENSE-PERCEPTION. 23 

material thing which is not a part of our bodies, that 
which is touched does not return the feeling which is 
experienced in the touching part, say the hand. 

Neither is the idea of extension furnished by the sense 
of touch. The contrary has been earnestly maintained 
by some writers, but cannot be substantiated. It is 
claimed, indeed, that as every extended body when in 
contact is felt over a certain surface of the bodily organ- 
ism, extension must be cognized by touch alone. This 
contradicts facts which any one may easily establish by 
experiment. If a person is blindfolded, and the hand 
laid palm upwards upon the table, the palm may be 
pressed by substances presenting plain surfaces but a 
great variety of forms and sizes, and the blindfolded 
man has no power to discriminate the forms and sizes of 
the touching bodies. He cannot distinguish a triangle 
from a circle, a surface of a half square inch from one of 
an inch square, or an oblique parallelogram from a rec- 
tangle. In order that any of these discriminations may 
be made, it is necessary that the hand or finger should 
be moved over the touching surface and trace its out- 
lines. This experiment is decisive. 

Neither is it possible for the mind to discriminate with 
any degree of accuracy the part of the surface of the 
body at which the contact takes place. All the power 
of discriminating the part of the body touched which we 
ever acquire is evidently gained by experience, and never 
makes any considerable approach to accuracy. If we 
have any irritation on some part of our bodies which is 
inaccessible to our eyes, we can only place our finger 
upon the irritated point by successive trials. 

§ 17. It is claimed by some that we judge of the ex- 
tension of the touching surface by the fact that there are 
two or more nerve-terminations embraced within it. 



24 SENSE-PERCEPTION. 

This can hardly be sustained. It is true that the nervous 
system is ramified so as to reach every part of the living 
organism, and that these nerve-termini are more numer- 
ous in some parts of the body than in others. It is also 
true that those parts of the surface of the body in which 
the nerve-termini are most numerous are proportionally 
more sensitive to contact. But this does not affect th e 
question we are considering. Those parts of the body 
in which the nerve-termini are most numerous, as the 
lips or the ends of the fingers, have no more power, 
without the aid of motion, of discriminating the form or 
size of the touching body, or the precise place of con- 
tact, than those parts of the body which are less sensi- 
tive to contact, because furnished with fewer nerve- 
termini. In all cases, whether the sensibility of the 
parts be great or small, motion is equally a condition of 
such discrimination. The infant while learning to make 
these discriminations knows nothing of nerves as a cause 
of sensibility, and of course knows not whether a given 
contact embraces one or many nerve-termini. How then 
can this consideration enable him to appreciate the 
extension of the touching body ? 

Even in mature life, we never acquire the power to 
discern the contact of an external body with the surface 
of our own by what is called the sense of touch, with 
any degree of certainty. We are often ourselves at a 
loss to determine whether an excitement experienced on 
the surface of our bodies is caused by external contact 
or an irritation from some unknown cause. Undoubt- 
edly the quick general sensibility of the surface of our 
bodies to external contact is of great importance to our 
welfare. It gives us warning of the presence of ene- 
mies, yet so gently as to inflict no pain, in the most 
unobtrusive manner. It excites us to attend to that 



SENSE-PERCEPTION. 25 

which needs attention, and to put forth the activity 
which the present exigency requires ; but it cannot be 
claimed that either the idea of contact or the idea of 
resistance or hardness is exclusively furnished by the 
sense of touch, as the idea of sound is by the sense of 
hearing. 

§ 18. It may perhaps be claimed that our notion of 
the outline and limits of our own bodies is derived from 
the sense of touch. But we learn the form of our own 
bodies and distinguish their limits in the same manner, 
in all respects as we do those of any other solid body. 
We learn to distinguish the different sides of our own 
bodies by moving the hands from one side to the other, 
just as we would learn to distinguish the different sides 
of a stone or a block of wood. There is indeed a pecu- 
liarity in our knowledge of the relation of the different 
parts of our body to each other which does not pertain 
to our knowledge of any body but our own. But this 
peculiarity is purely the result of experience in connec- 
tion with voluntary motion, and muscular and general 
sensibility. In early childhood we remember to have 
had great difficulty in distinguishing the right hand 
from the left or the right side from the left side. But 
we learned in time so to distinguish both the muscular 
and the general sensibility of one side from those of the 
other, as to know the right hand from the left under 
all circumstances, by an instantaneous judgment. This 
judgment, however, is not founded in any peculiar 
manner on that general sensibilty which we call touch, 
but more especially on the muscular sensibility of the 
two sides which we have learned by experience to dis- 
criminate from each other. In early childhood when I 
wished to distinguish my right hand from my left, I 
used to look for a scar which I knew was on my right 
5 



62 SENSE-PERCEPTION. 

hand. A few years later in life I could distinguish by 
an instantaneous judgment without looking for the scar. 

In the same manner we learn to estimate distance 
without the aid of the feeling produced by contact. 
We have already seen that the idea of distance is sug- 
gested by the experience of the motion of our own 
limbs or bodies, and our consciousness of producing 
those motions by the action of our own muscles. We 
estimate distance by the amount and continuance of the 
muscular effort required. A lady was once reported, on 
taking her seat for her first journey by rail to the dis- 
tance of seventy-five miles, to have taken out her knit- 
ting and commenced work. When the station which 
was to be the end of her journey was announced, she ex- 
claimed with surprise, " if I had known it was no further 
I would have walked." She had judged of the distance 
by the amount of muscular effort she had made with her 
fingers upon her knitting needles. So the child always 
judges of distance. If the distance is not greater than 
can be compassed by the thumb and fingers of one 
hand, or by stretching the two hands, the movement of 
the hands forms the standard. If greater than can be 
so compassed, the feet and the motion of the whole 
body must be resorted to as a standard of distance. 
The child never learns the meaning of the word mile 
till he has become accustomed to walk a mile. It is 
thus made apparent that all our ideas of distance origi- 
nate, not in the action of the senses but in the exercise 
of our power of voluntary motion. 

§ 19. In view of all these considerations, it seems im- 
possible to admit the existence of any thing in the hu- 
man constitution which can be properly called the sense 
of touch. In taking this position we are not entirely 
alone. The suggestion is not entirely new. But we 



SENSE PERCEPTION. 27 

are painfully aware that the weight of authority is 
overwhelmingly against us. Some of the ablest wri- 
ters have not only felt no hesitation in classifying touch 
with the special senses, but have given it preeminence 
among them, and spoken of it as the leading sense. If 
this be an error, as we suppose, writers have fallen into 
it by failing to define their language. They have in- 
cautiously ascribed to the sense of touch ideas, of tem- 
perature, weight, and distance, and even of pain and 
lesion, which certainly have a very different origin.* 

There is also another consideration which strongly 
tends to the same conclusion. If there is a sense of 
touch which is to be ranked with the other special 
senses, it has no emotional function, as it has already 
been remarked all the other senses have. It does not 
open to the soul any peculiar source of happiness 
superadded to its practical uses, as the other senses do. 
If it could be shown that our ideas of form are derived 
from the sense of touch as our ideas of color are from 
the sense of sight, it might perhaps be claimed, that the 
sense of touch is to a considerable extent the source of 
our conception and enjoyment of beauty. But it has 
already been shown, that our idea of form has another 
origin, that it comes through the action of the muscles 
and not through the sense of touch. In addition to 
this, even if it should be admitted that our idea of form 
is derived from the sense of touch, it would still remain 
true, that our conception of the beautiful in form comes 
chiefly through form as presented to the eye, rather 
than as presented to the touch. How far the man who 
has always been destitute of eye-sight is capable of 
appreciating and enjoying the beautiful in form, it is not 
perhaps easy for seeing men to determine. But surely 

* Reid's Collected Writings, p. 119 and onwards. 



28 SENSE-PERCEPTION. 

he must have that power in a very limited and low 
degree, if in any degree at all. What can St. Peter's 
at Rome or any of the great architectural structures of 
the world, or even the noble human form be to the blind 
man, as compared with what it is to one who is fully 
endowed with the sense of sight ? It seems to us then 
impossible to classify the feeling produced by external 
contact «of our bodies, with the special sensations. For 
convenience we shall hereafter use the feeling of contact 
instead of the sensation of touch. 



CHAPTER IV. 



Examination of the Special Senses. Sight. 

§ 20. In proceeding to the examination of the special 
senses, there are decisive reasons for first directing our 
attention to the sense of sight. It is but a very meagre 
and barren conception of this universal frame of things 
with which the mind becomes acquainted by those pro- 
cesses which we have thus far considered, and it is 
chiefly by the aid of the sense of sight that this outline 
is filled out, that this dry skeleton is clothed with flesh 
and sinews and filled with life and beauty. It is this 
sense more than any other which enlarges our knowl- 
edge of this material universe, till the definiteness of 
knowledge is lost in the indefinite wonder which the In- 
finite inspires. At the point of this discussion at which 
we have now arrived, the mind is prepared for this en- 
largement, and will be the better fitted for the interest- 



SENSE-PERCEPTION. 29 

ing details furnished by the other senses, after having 
taken in the comprehensive sweep of the universe which 
the noble sense of sight renders possible. 

The special organ of the sense of sight is the eye. 
This is an exquisitely constructed optical instrument, 
and the model after which all the optical instruments 
having for their object to assist vision are modeled. 
For a description of its structure, we must refer the 
student to the treatises on anatomy. It is only neces- 
sary here to remark, that the one design of the delicate 
and refined structure of the eye is, to form a clear and 
exact image of all material objects in the field of vision 
on the retina, which is a network of nerves situated in 
the back part of a cavity, in the front part of which the 
eye is situated. The image is formed by the refraction 
of light, according to laws which are familiar to every 
optician, and which therefore we need not here explain. 
Every material object reflects more or less of the light 
which falls upon it. A portion of the light so reflected 
enters the eye through the opening in its front called 
the pupil, passes through a most delicately constructed 
system of lenses, where it undergoes a refraction which 
brings the rays to a focus on the retina, by which means 
an image of the object from which they are reflected is 
formed. The retina or screen on which this image is 
received is a network formed by ramifications of the 
optic nerve or nerve of vision. 

§ 21. Thus far we are able to trace the process of 
vision on purely optical principles, precisely as the opti- 
cian traces the formation of the image on the screen of 
the camera obscura. Beyond this point the optician can 
render us no aid toward the solution of the problem of 
vision. We here meet a fact which we must accept as 
ultimate, that when such an image is formed on the ret- 



30 SENSE-PERCEPTION. 






ina of the eye, vision follows. On the other hand, no 
vision can be produced otherwise than by forming such 
an image on that one pair of nerves, no other nerve in 
the body will answer the purpose. On this one pair of 
nerves the image must be formed, or no vision can take 
place. These facts we say are ultimate, and are deter- 
mined only by experiment. We have said that when 
such an image is formed on the optic nerve under nor- 
mal conditions, vision will take place. Yet if that be 
the optic nerve of a newly born infant, vision will not 
take place. No knowledge of the objects in the field of 
vision, however perfectly represented on the retina, will 
be conveyed to the mind. A rational soul must first in- 
tervene, and acquire the power of interpreting the indi- 
cations of that image, so as from it to take cognizance 
of the object from which it comes. Till a rational soul 
has thus interpreted that image, it can convey no intel- 
ligence to the mind. The question we have to solve, 
then, is, by what steps and processes the soul acquires 
the power of interpreting this image, so as to learn from 
it the qualities and powers of the external universe, 
which when interpreted it does represent to the rational 
mind. We must next endeavor to answer this question. 
§ 22. I. The peculiar class of ideas which the mind 
acquires by this sense is light, in all its modifications of 
color and shade. But to furnish the mind with this class 
of ideas in all their delicacy and beauty, by no means 
exhausts the function of this sense. The eye not only 
paints with inimitable minuteness and delicacy of detail 
on the optic nerve a picture of the material universe, 
but furnishes the mind with a system of arrangement by 
which, by the study of this picture, the rational soul 
comes to know that universe. The full function of the 
sense is to enable the soul to know the external world 



SENSE-PERCEPTION. 31 

by means of a colored picture of it on the optic nerve. 
The eye is the painter, the photographer, the mind inter- 
prets the picture by means of the muscular organization 
with which the eye is furnished. 

II. Though the eye is certainly capable, by its own 
voluntary motion, of forming a rudimentary notion of 
extension and place, in the manner already described, it 
is not capable of forming the idea of outness. It is not 
conceivable that this should be furnished otherwise than 
by the experience of resistance to the soul's conscious 
power of voluntary motion. It is not easy to conjecture 
how it is possible for such resistance to be consciously 
experienced through the motions of the eye. We must 
go back to the very point from which we commenced 
our inquiries into the results of the muscular sensibility. 
We there saw how the mind does, in the motion of the 
hands or other limbs or parts of the body, experience 
such resistance, and learn from that experience the pres- 
ence of a resisting non-ego. We here call attention to 
the fact that the mind has or is liable to have a triple 
experience at the same instant. While the attention is 
fixed on the resisting non-ego, a feeling of contact and a 
sensation of color are likely to be experienced, and can- 
not long fail to attract the mind's attention. While 
voluntary motion resisted gives a non-ego, the cessation 
of that motion gives place, and to that place the mind 
refers the feeling of contact and the sensation of color, 
and comes to regard them as products of the causal 
power of the non-ego. The action of the mind therefore 
in referring the sensation of color to an external resist- 
ing cause is dependent on the action of the muscular 
sensibility. If the mind had not learned through the 
muscular sensibility the existence of the resisting non- 
ego, it never could have acquired the notion of an exter- 
nal surface or body. 



32 SENSE-PERCEPTION. 

§ 23. It has been maintained by some writers that the 
eye gives the notion of an extended surface directly 
without any dependence on voluntary motion, and that 
the sensation of color necessarily implies the existence of 
the idea of extension.* They suppose that the connec- 
tion in our minds of color with an extended surface is 
not formed by experience, but is natural and necessary. 
To us on the contrary it seems that the idea of extension 
is necessarily derived from the activity of the soul in 
voluntary motion. All the varying sensations of color 
are certainly produced by the impression of variously 
modified light on the nerve of vision. Each modifica- 
tion of the light produces by its direct action on that 
nerve a corresponding variation either of color or shade. 
If the human body were as motionless as a marble 
statue, the constitution of the eye remaining in the same 
relation to the knowing mind, as now, it can hardly be 
supposed that there would not be changes in the sensa- 
tions corresponding to every change in the light that 
fell on the retina of the eye. Doubtless the change from 
day to night and from night to day, from the green of 
spring and summer to the white of the snow-clad land- 
scape of winter would be noticed just as now. Would 
the landscape also be known as extended ? Would its 
different colored and shaded localities be distinguished 
from each other? Would a mind thus limited in its 
control of the bodily organs distinguish one place from 
another, and apply the words here and there to the dif- 
ferent points of the view ? Let the supposition be made 
that a circular disk were placed before an entirely un- 
trained eye, painted with parallel bands of strongly con- 
trasted colors^ would the mind necessarily distinguish 
the different bands of color from each other and thus 
recognize the disk as extended ? 

* Porter's Elements, Sec. 101. 



SENSE-PERCEPTION. 33 

To this it may be replied, that in such a case, neither 
the disk nor the bands of color painted on it would be 
distinguished by the untrained mind, from the other 
objects in the field of vision. In order to make a test 
case, it would be necessary to suppose, that the un- 
trained eye is in a dark room, and that the colors were 
in stained glass filling an opening in the shutter, so that 
no light could enter the eye except through the stained 
glass. Would then the eye, however untrained, distin- 
guish the bands of color and locate them each in its 
proper place, and thus recognize the extension of the 
surface of stained glass on which they were painted ? 
Would a motionless eye ever do it ? 

§ 24. I had not long ago my attention called acci- 
dentally to a fact which seems to answer the question. 
In a room in which I pass a good deal of time, a varie- 
gated flower bloomed. The ground was a very pale 
pink, while scattered irregularly over the petals were 
patches of deep red, not shaded into the ground, but 
abruptly contrasted with it, and separated from it by 
sharp and definite and in some cases straight lines. To 
a spectator standing near the flower these definite lines 
were easily traced with the most perfect distinctness ; 
but on removing the eye to a considerable distance, not 
only was it impossible to distinguish the patches of deep 
red from the pale pink of the ground, but the whole 
flower appeared of a uniform color, which was neither 
the pale pink of the ground nor that of the red patches, 
but a compromise between them, being evidently the 
color which would result from a combination of all the 
colors of the flower. So soon as by reason of distance 
the eye was no longer able, by the motions of its own 
axis, to trace the lines which separated the red from the 
pale pink, it lost its power of distinguishing the colors 
which all ran together into one compromise color. 

6 



34 SENSE-PERCEPTION. 

This is exactly what would take place, if the piece of 
painted glass were placed before an eye incapable of mo- 
tion in the shutter of such a dark room as supposed. 
The separate colors could not be distinguished from 
each other, but all would be blended into a mixture in 
due proportions of all the colors present. Our assertion 
is made true, that, to such a motionless eye, a variously 
colored landscape would appear as colored; but no 
sharp distinctions of contrasted color would be made. 
All the colors present to the eye would appear as a con- 
fused mixture. Would then this confused sensation of 
color suggest to the mind the idea of an extended sur- 
face ? There is no apparent reason to think so. Cer- 
tainly the different patches of color would not be dis- 
tinguished from each other, and no idea would be formed 
of their relative situation in the landscape. The idea of 
externality may not have been yet originated. The 
sensation of color may have been purely subjective, not 
suggesting to the mind any notion of external surface 
or body at all, like a flash of light the origin of which 
the mind forms no conception of. The sensation may 
be permanent, but as devoid of any association with an 
extended surface as the eye is of motion. 

§ 25. III. As it was shown in a former chapter how 
the continuity of resistance to voluntary motion leads to 
the notion of the line and the surface, it might be shown 
that the continuity of the sensation of color in connec- 
tion with the voluntary motion of the axes of the two 
eyes over any colored surface, might lead the mind to 
the same notion, as readily as it was lead to it by the 
muscular sensibility in connection with the motion of 
the hand. In the same manner if the surface was vari- 
ously colored, the motion of the axes of the eyes over 
all parts of the surface would enable the mind to dis- 



SENSE-PERCEPTION. 35 

tribute the various colors to their own proper points 
in it. 

IV. When however the mind is to pass to the con- 
sideration of the third dimension of extension, so as to 
form the notion of planes at an angle with each other 
and of solid bodies, it must again fall back upon the 
process of voluntary motion cooperating with the mus- 
cular sensibility. No action of the eye and its muscles 
can furnish the mind with the notion of two planes at 
an angle to each other or of a solid angle. At that 
point the whole mental movement seems to be neces- 
sarily dependent either on the muscular sensibility or 
that general sensibility of the surface of the body which 
is generally called the sense of touch. 

The same may be said with equal truth of all curved 
lines and surfaces. The mind seems incapable of form- 
ing an idea of such surfaces otherwise than through the 
continuity either of contact or of muscular sensibility, 
in connection with voluntary motion which is con- 
stantly changing its direction, which change of direc- 
tion is discerned only through the muscular sensibility. 
The muscles which move the eye are not capable of dis- 
cerning these delicate changes in the direction of the 
motion without also experiencing at the same time the 
resistance of the non-ego. That resistance is never en- 
countered by the muscles which move the eye. It is 
not true that we ever get the notion of a curved surface 
through the general sensibility of the surface of the 
body, but it is true that we cannot get that notion with- 
out the experience of resistance to the action of the 
muscles. We may therefore generalize the proposition 
that we are dependant on the muscular sensibility at 
last for all our ideas of the form of bodies. 



36 SENSE-PERCEPTION. 

§ 26. V. When however the notion of angular and 
curved surfaces has been formed in the appropriate man- 
ner, the eye furnishes the mind with the means of dis- 
criminating the different forms of bodies from each 
other with great rapidity and facility, without appealing 
again either to contact or muscular sensibility. It is 
the province of the eye, out of the light which comes 
from any object, to construct an image of that object, 
and an image formed from a plane surface is distin- 
guished by different modifications of light and shade 
from one which is formed from a curved or angular sur- 
face. The mind soon acquires the power of discriminat- 
ing between the images so formed, by studying the 
image of any surface in connection with the muscular 
and general sensibilities experienced in connection with 
it. Thus the image which the eye forms from a plane 
surface is recognized as such, as soon as it appears on 
the retina, and so of the images of curved and angular 
surfaces. 

VI. The question has been much discussed, what is 
the natural place of the visual object with reference to 
the eye ?* The answer doubtless is, that there is no nat- 
ural place for it. The mind cannot place it, except by 
the aid of the muscular sensibility in connection with 
voluntary motion, especially that of the hands. As 
already shown, the experienced resistance is first referred 
to something external, then the color is referred to the 
same external something, because it is experienced sim- 
ultaneously with the resistance of the non-ego, and is 
therefore referred to the same external cause. The 
sensation of color accompanies and becomes inseparable 
from the conception of a plane, curved or angular sur- 
face, and finally the distance of each particular surface 

* Reid's Collected Writings, pp. 163, 164. Porter's Elements. Sec. 
101. 



SENSE-PERCEPTION. 37 

or part of a surface is determined by the muscular effort 
necessary to move the hand, or the feet when they must 
be used, so as to bring ourselves in contact with it. 
These distances the mind soon learns to estimate with 
tolerable correctness without any appeal to contact or 
the muscular sensibility. This point and several others 
which we are here compelled to allude to, will be more 
fully illustrated under the head of the Cooperation of 
the Senses. 

§ 27. VII. Two other questions have seemed to many 
to present no small difficulty. The image on the retina 
is always inverted and by optical laws must be; why 
then is the object seen, not like the image, inverted, but 
erect ? There is always an image formed on the retina 
of each eye ; why then, as two images are seen, is not 
the object seen as double ? Nearly the same considera- 
tions answer both these questions.* 

It is only through the discoveries of comparatively 
recent science that any of us know that we do see by the 
aid of an image on the retina. Men saw just as perfectly 
before that discovery was made as they do now, and 
little children that know nothing of the retina and the 
image on it have just as perfect vision as the philoso- 
phers who have studied the anatomy of the eye. Of 
course, as they do not know that there is any image, 
neither do they know whether that image is erect or 
inverted, and its position can have no influence on the 
judgment they form of the position of the object. The 
judgment of erectness or inversion is formed in quite 
another manner. When an object is before the eye we 
learn by experience only that in order to see one part of 
it we must turn our eyes upward, and in order to see 
another part of it we must turn them downwards. The 

* Porter's Elements, Sec. 100, 101. 

7 



38 SENSE-P RECEPTION. 

former is regarded as the top and the latter as the bottom 
of the object. This judgment is confirmed by our expe- 
rience in the use of our hands or other parts of the body. 
If the object is so near and of such size that it can be 
examined by moving the hand over and along it, we 
must move both our hands and our eyes upwards to reach 
the top and downwards to reach the bottom. Thus only 
the question of top and bottom is determined, and in the 
same manner the question of right and left. In neither 
case is the erectness or the inversion of the image taken 
into consideration at all. Motion alone is appealed to. 

As we do not know that there is any image on the 
retina, so we do not know that we have an image on the 
retina of each eye. The fact of a double image can then 
have nothing to do with our notion of the object as 
single or double. That too is determined in quite another 
manner. We measure the situation of an object with 
both hands, if we are blind, and if each hand finds the 
object in the same place, and affecting our sensibility in 
the same manner, allowing for difference of situation in 
the two hands, then we recognize the object as single, 
examined by two hands. In precisely the same way, we 
examine the object in all respects by each eye, allowance 
of course being made for the different positions of the 
eyes, and finding both eyes making the same report, we 
judge that it is one object seen by both eyes. 

Sometimes a single object seen by the two eyes will 
appear double. When the axis of each eye is directed 
toward the same point in space, an object situated at 
that point will be seen single; but if the axes are not 
directed toward the same point where the object is situ- 
ated, but toward some other point, then the object will 
be seen double. The reason is, that when we are look- 
ing at a single object with both eyes we invariably turn 



SENSE-PERCEPTION. 39 

the axis of each eye toward the same point in the object 
we are looking at. If then we see an object with the 
eyes fixed on some point not in the object, we shall see 
it double. This takes place in some forms of disease, in 
which the will loses the control of the muscles of the eye, 
so that the axes of the two eyes cannot be at will turned 
toward the same point. A like illusion may also some- 
times be practiced upon us through contact. If the fore- 
finger and the second finger of the hand be crossed, and 
a pea be placed between them, we shall feel two peas 
where there is but one, because that in our normal expe- 
rience we cannot feel the same pea on the opposite side 
of these two fingers. All such judgments are determined 
by comparing our present experience with that which is 
usual and normal ; and when the experience is abnormal, 
an erroneous judgment is apt to be formed. These facts 
certainly do prove decisively that all our sense-percep- 
tions are founded on an act of judgment which is subse- 
quent to the sensation, and depending on experience. 
The more carefully we examine all the facts of sense- 
perception, the more will this be confirmed as a truth. 

§ 28. IX. In the first outlook of the infant mind upon 
the material universe, all the objects which are in the 
view at any one time are not seen as individual objects, 
but as one whole, and it is only by experience very 
gradually acquired that particular objects are separated 
from that whole and known in their individuality. For 
example, the chairs, the tables and other articles of fur- 
niture of an infant's room, are seen as projected upon the 
same plane, and are only recognized as several patches 
of color on that plane. They are seen just as the painter 
must see them, in order to represent them correctly upon 
his canvas. The objects which are frequently moved 
are first detached and individualized. The child is also 



40 SENSE-PERCEPTION. 

aided in this process by being himself removed to differ- 
ent parts of the room, being thus enabled to see the 
objects from different standpoints and in different rela- 
tions to each other and to the permanent parts of the room. 
This process is gradually carried on till all the individual 
objects are recognized as such. The same process is 
extended to the whole outer world. Many objects which 
are really distinct are regarded as one by the inexperi- 
enced child and the savage. A savage who had never 
seen a horse, on seeing a man of new and strange features 
riding on horseback, regards the man and the horse as 
one animal, and contemplates it with indescribable terror. 
This separation of the material universe regarded as a 
whole has to be extended to the distant heavens, and 
the completion of it is among the last and highest tri- 
umphs of science. 

X. Before leaving the subject of vision, it is appro- 
priate to remark, that the sense of sight not only has this 
power of vastly extending our knowledge of the material 
universe beyond all which could have been possible with- 
out it, but that it also invests us with the power of read- 
ing at a glance the minds, hearts and characters of our 
fellow-men. Every change in the feelings, the thoughts 
and intentions of our associates is almost sure to manifest 
itself in the eye, the gestures, the features of the face 
and the attitudes of the body. Many of these we learn 
by experience to interpret and understand. Many of 
them are however entirely outside the field of sense- 
perception, being wholly spontaneous in their manifesta- 
tion, and dependent, not like the special sensations for 
their interpretations, on experience and rationality, but 
on natural and instinctive intuition. All acquisition of 
knowledge is the result of rationality acting through 
experience, but feeling is spontaneous in its origin, and 






SENSE-PERCEPTION. 41 

instinctive in its expression and interpretation. A large 
portion of this spontaneous intercourse of the feelings is 
carried on through the sense of sight. 



CHAPTER V. 



Examination of the Special Senses. Sense of 
Hearing. 

§ 29. Next in the natural order of the development of 
our subject is the sense of hearing. As the sense of 
sight not only furnishes the mind with a new class of 
ideas not attainable by us through any other source, but 
greatly enlarges the sphere of our possible knowledge of 
the external universe, so the sense we are next to exam- 
ine both furnishes to the mind a peculiar idea, and opens 
up sources of knowledge which could not have been 
reached by the eye. By the last-named sense, we can 
learn nothing of objects in the absence of light, or when 
an opaque body is between the eye and the object. 
These are very serious limitations on our power of 
becoming acquainted with the objects around us. By 
the ear these limitations are removed. 

As color and shade comprehend all the ideas which 
are revealed to the mind through sight, so the word 
sound embraces all those which come through hearing. 
In respect to all these ideas, a mind that is deprived of 
this sense must remain utterly blank. A great number 
of persons in every generation are either born destitute 
of this sense, or are deprived of it by the accidents to 



42 SENSE-PERCEPTION. 

which early childhood is exposed, and as all oral lan- 
guage is addressed to the ear, such persons never acquire 
the power of speech. They are not only deaf but mute. 
The results which have been attained in recent times by 
the education of deaf-mutes demonstrate, that not only 
might the human race have existed under these condi- 
tions, but that had all men been from the beginning 
without this sense, society might have existed and civil- 
ization to a certain extent attained. Even in such a 
silent world the rational soul might have devised means 
of carrying on intercourse by a lauguage addressed to 
the eye and not to the ear ; but under what limitations 
of the possibility of human thought and culture ! 

§ 30. The peculiar organ of this sense is the ear. For 
a scientific description of this organ, we must refer the 
student to the treatises on anatomy and acoustics. He 
will there learn that as the design of the optic apparatus 
of the eye is to form a colored image of the external 
object upon the optic nerve, to be the soul's instrument 
of vision, so the design of the exquisite structure of the 
ear is, to cause the sound to be repeated upon the rami- 
fications of the acoustic nerve which are situated in the 
inner chambers of the two ears, which repetition of the 
sound is the soul's instrument of hearing. In order to 
render this perfectly intelligible it is necessary to state 
that all sonorous bodies, that is all bodies capable of 
causing the sensation of sound, are also capable of being 
made to vibrate by a blow or concussion. In order that 
the sensation of sound may be experienced, this vibra- 
tory motion must in some manner be communicated to 
the acoustic apparatus of the ear, and by it repeated 
upon the acoustic nerve. 

It is important to notice how close is the analogy be- 
tween the structure of the ear and that of the eye. In 



SENSE-PERCEPTION. 43 

every case of sensation, through any one of the senses, 
there must be either contact of the external substance 
with the organ of sense, as in the case of taste, or else 
some medium of communication between the object and 
the organ, as in the cases of sight, hearing and smelling. 
In vision, the medium is light, in hearing it is atmos- 
pheric air, or some other substance to which the vibra- 
tory motion of the sounding body is communicated, and 
by it borne and imparted to the tympanum and through 
it and the apparatus of the inner ear, to the acoustic 
nerve. The analogy referred to may then be noticed 
step by step. The tympanum of the ear corresponds to 
the pupil of the eye, the interior apparatus of the ear to 
the lenses of the eye, the acoustic nerve in the inner 
chamber of the ear to the retina of the eye, and the 
impressions of the vibrations of the sounding body to 
the image on the retina. In both cases perception is 
brought about through an exact miniature representa- 
tion of the object on the nerve of special sensation, — on 
that nerve and on no other in the whole body. As in 
the case of seeing, so in that of hearing, on the fulfill- 
ment of this condition sensation will take place, and 
perception, provided that organism is inhabited by a 
rational soul that is attentive, and has learned by expe- 
rience and its own activity to interpret its own sensa- 
tions. It is our next task to trace the steps by which 
that rational soul, at first utterly unable to gain any 
information from this sense, any more than from sight, 
gradually acquires the power of interpreting the sensa- 
tions of the ear, so as by means of them to enlarge the 
boundaries of its knowledge of the material world. 

§31. I. Previous to experience, this sensation is 
purely subjective. The mind has no power of referring 
it, either to an external object as its cause, or to the 



44 SENSE-PERCEPTION. 

organ in which it is experienced. Not only does the 
mind at first fail to refer this sensation to the acoustic 
nerve situated in the interior chamber of the ear, where 
only it is experienced, but even in mature life, after 
science has informed us what the seat of the sensation is, 
we have still no consciousness of experiencing it at that 
point. We learn by experience to refer it in general to 
the ear, because a sounding body must be brought as 
near as possible to the ear in order to hear it most loudly. 
Without this experience to guide us, we should not know 
even in mature life, till informed by science, that the ear 
has any more connection with it than the rest of the 
body. Much less have we the power of referring it to 
any external cause. 

II. Before it can be referred either to its proper place 
in the organism, or to an external cause, the ideas of 
extension, of extended surfaces and of bodies external to 
ourselves, must have been formed in the manner already 
described. This sense is conditioned by the previous 
intelligent use of the muscular sensibility and of volun- 
tary motion in the same manner as the sense of sight. 

III. The mind learns to refer sensations of hearing to 
their proper external causes by a succession of experi- 
ments. Some external body with which the learner is 
already acquainted is brought in collision with some 
other body, and a peculiar sensation is immediately 
noticed. The same sensation is produced again and 
again in the same circumstances, till he has learned that 
that body will on being struck produce that sensation. 
The same course of experiment is gone through with in 
respect to other sensations of sound, till he has learned 
to refer them each to the sonorous body by which it is 
produced. Thus in each and every case a sensation of 
sound is converted into the appropriate perception. 



SENSE-PERCEPTION. 45 

The situation of the sounding bodies with respect to the 
ear is ascertained in all cases by the muscular sensations, 
aided in seeing persons by sight. 

§ 32. IV. The ear and the eye estimate the direction 
and distance of objects in almost the same manner. In 
vision the object is seen in the direction toward which 
the axes of the eyes must be turned to see it most dis- 
tinctly. The axes of the eyes are directed toward the 
object, either by turning the eye in its socket, or by 
turning the head on the joint of the neck, or by a move- 
ment of the whole body, or by all these together. In 
the case of the ear, the movement of the head and of the 
whole body only are available, the ear having no motion 
of its own. The sounding body is judged to be in the 
direction toward which one of the ears must be turned, 
to hear the sound most loudly and distinctly. Our judg- 
ments of direction through the ear are much less accu- 
rate than those formed through the eye. The reason is 
that the muscular organization for giving direction to 
the ear is much less delicate and perfect than that by 
which the eye is directed toward its object. 

The eye has many modes of estimating distance. 
Some of these are not available to the ear. When the 
eye is left to its own resources to judge of distance by 
the image on the retina, its method is much the same as 
that which is used by the ear. In such a case the eye 
judges of the distance by the distinctness or dimness 
with which the detail of the picture is filled out. In 
the same manner the ear gives distance, not so much by 
the loudness as by the distinctness of the sound. In 
sounds which are near at hand, there are apt to be mi- 
nute varieties of sensation which would be inaudible at 
a greater distance ; but at best our judgments of dis- 
tance by the ear only are very uncertain. 



46 SENSE-PERCEPTION. 

§ 33. V. As an instrument to be used in acquiring a 
knowledge of the material universe, the ear can bear no 
comparison with the eye. The distance at which any 
sounds can be heard by the unassisted ear is only a few 
miles, and even by the aid of recent inventions, it can 
only be extended over a very small portion of our 
planet ; yet the unassisted eye discerns the existence of 
objects in remote portions of the universe, in contem- 
plating whose distances from us the mind is over- 
whelmed and confounded. All the information which 
hearing can give us of the various material substances 
around us is confined to their power of causing the sen- 
sation of sound when coming in collision with other bod- 
ies. Of size and form, it cannot be trained to give us 
any information, and as we have seen, its indications of 
direction and distance are very vague and uncertain. 

On the other hand, however, its power of giving us a 
knowledge of the feelings, intentions and characters of 
our fellow-men by direct intimation is not at all inferior 
to that of the eye. If it is true that every purpose, 
feeling and passion of the soul is likely to manifest 
itself in the faces and gestures of men, it is equally true 
that they are even more sure to express themselves in 
tones of the voice, which are natural signs of feeling 
and character, instinctively uttered and instinctively 
interpreted. Emotion has a natural language both of 
the eye and of the ear. Perhaps that addressed to the 
ear is the more expressive and the more easily under- 
stood. It is also worthy of notice, that to some extent 
at least, this natural language is common to us with the 
brute creation. Especially is this true of the expres- 
sion of emotion by sounds. The semi-tone proceeding 
from her offspring reaches the heart of the brute as of 
the human mother. 



SENSE-PERCEPTION. 47 

In this chapter and in the chapter on the sense of 
sight, it has been our object for the most part to discuss 
these senses only so far as they are instruments of per- 
ception, whereby the soul learns to understand the ma- 
terial universe. There are other functions of these 
senses to be discussed in future chapters. 



CHAPTER VI 



Examination of Special Senses continued. Smell 
and Taste. 

§ 34. It is by the sense of sight and hearing for the 
most part, that man acquires a knowledge of the uni- 
verse in which he lives. By the muscular sensibility, 
the feeling of contact and the act of voluntary motion, 
he learns the existence of an extended and external uni- 
verse, and by the aid of the senses of sight and hearing, 
he fills in that knowledge with an endless variety of rich 
and interesting detail, and extends it on all sides far out 
towards the limits of existing material things. 

The two senses remaining yet to be considered have 
for the most part reference only to limited classes of 
objects, and stand related to the preservation of life, 
and, if we embrace along with them the sense of sex, 
to the preservation of the species. It is also to be no- 
ticed that, in dealing with these senses, we have forced 
upon our attention another function of sensation, which 
has nothing to do with sense-perception, and of which 
we have thus far made only very brief mention. It is 



48 SENSE-PERCEPTION. 

to furnish man with almost boundless sources of delec- 
tation, and to lay in human nature itself the foundation 
of esthetics. All the senses are sources of exquisite 
pleasure, superadded for the most part, it would seem, 
to what was really necessary for the practical uses to 
which the senses were to minister. This is now only 
named, that we may not seem to be neglectful of it. 
This function is conspicuous in the senses which remain 
to be examined. 

§ 35. The sense of smell next demands our attention. 
This sense is more analogous to those of sight and hear- 
ing than taste, because by it we may be still dealing 
with objects which are at some distance from the organ 
through which the sensation is experienced. The odor- 
ous object is very rarely in actual contact with the 
organ, and the sense is capable of acting through a con- 
siderable intervening space. 

Its organ is situated in the nostrils, and is a ramifica- 
tion of the nerve of smell spread over a certain portion 
of those cavities in a manner very analogous to that in 
which ramifications of the optic and acoustic nerves line 
the interior of those chambers. The medium through 
which the olfactory nerve communicates with the odor- 
ous body consists of certain particles of the substance of 
that body which escape into the surrounding atmos- 
phere, and find their way to the organ of smell. If this 
is a true account of the matter, the substance of all 
odorous bodies must be more or less volatile, and capa- 
ble of diffusing itself through the surrounding air in 
exceedingly minute division. If this is the true origin 
of odors, as probably it is, there are two reasons why 
the organ of smell ought to be situated just where it is. 
As we are continually breathing the air, in which we are 
at all times immersed, the particles of any odorous body 



i 



SENSE-PERCEPTION. 49 

which may be diffused in the air around us are sure to 
be drawn into the nostril, and thus be brought into con- 
tact with the organ. One of the functions of this sense 
is to test the quality of the air we are breathing, and 
to give us warning when it is vitiated by any deleteri- 
ous influence dangerous to our health and safety. All 
the air which is introduced into our lungs in breathing 
should, as far as possible, be introduced through the 
nostrils, and is thus subjected to the scrutiny of this 
sense. 

Another function of this sense is to scrutinize our 
food, to detect any deleterious quality in it, that it may 
be rejected before it is received into the mouth. It was 
therefore necessary that it should be so situated as to 
act as a sentinel at the opening of the mouth. It is then 
situated precisely as it should be, in order that it may 
exercise a watchful scrutiny over all our food, that noth- 
ing deleterious may find admission to the organs of 
digestion and assimilation. 

§ 36. As has been already remarked the sensations of 
smell are, previous to experience, purely subjective, not 
referred to the part of the organism where they origi- 
nate, or to any external cause.* In mature life, when 
experience has done all in the premises which it can do, 
none of us not instructed in the anatomy of the organ, 
knows precisely in what part of the nostril the nerve is 
situated, or how widely it is diffused. We have no 
consciousness of its situation, neither are we able to 
determine where or what the object is from which the 
odor comes without the aid of voluntary motion and the 
other senses. We are unable to decide by the sense 
alone, whether it is an odor widely diffused in the air 
from some unknown cause, or comes from some object 

*Dr. Thomas Brown, Lecture XX. Sense of Smell, p. 195. 
9 



50 SENSE-PERCEPTION. 

near at hand. Nor can we determine in most cases the 
direction from which it comes, though in some cases we 
can form an imperfect judgment of the direction, by 
methods closely analogous to those used in the sense of 
hearing. All these points we are able to determine by 
the aid of voluntary motion and the other senses. The 
relations of the sensations of smell to perception are, 
therefore, precisely analogous to those of the senses 
hitherto examined. Perception may follow or may not, 
according as they are or are not attended by a rational 
soul interpreting the sensation by our muscular sensibil- 
ities and our acts of voluntary motion. 

§ 37. The perceptional function of the sense of taste is 
to apply still another test to whatever is about to be 
introduced into the stomach, to ascertain its fitness or 
unfitness for the nutrition of the body. It also has 
another function, to increase the inducement to take a 
sufficient supply of wholesome food by the added pleas- 
ure of the gratification of this sense in eating it. It is 
with the former of these functions only that we are at 
present concerned. 

The organ of taste is situated in the tongue, and some 
other parts of the mouth, which are furnished with a 
peculiar coating of nerves, which alone of all the nerves 
of the body can yield the specific sensation called taste. 
As the feeling of contact extends to the interior surface 
of the mouth, and as the sensation of taste can only be 
experienced by the actual contact of the substance 
tasted with the organ, the feeling of contact and the 
sensation of taste are both experienced at the same 
time.* This is not invariably and necessarily so. It is 
possible, by closing a person's eyes, to introduce into the 
mouth a small quantity of a highly sapid liquid, of the 
*Dr. Thos. Brown, Lecture XX. Taste, pp. 196, 197. 



SENSE-PERCEPTION. 51 

same temperature of the mouth, which will produce a 
very decided impression on the organ of taste, without 
exciting the feeling of contact at all. We often retain 
in the mouth the taste of some substance, after nothing 
of it remains in the mouth which can excite the feeling 
of contact. The sensations of taste and the feeling of 
contact are not therefore necessarily and universally 
simultaneous. 

The fact that we do so generally feel a substance in 
the mouth at the same moment that we taste it, and 
that all substances must be introduced into the mouth 
in order to be tasted, naturally lead the mind almost 
immediately to regard the sense of taste as situated in 
the mouth, and to refer the sensation to the food taken 
into the mouth as its cause. But our sensations of taste 
are not therefore any the less obviously, before experi- 
ence, purely subjective. Most of us pass through our 
whole lives without ever learning over what portion of 
the interior of the mouth the organ of this sense extends, 
and the experience of the sensation furnishes us no 
means of knowing what parts of the cavity are, and what 
parts are not, susceptible of the sensation. We do indeed 
early learn that the upper surface of the fore part of the 
tongue is susceptible of it ; but we learn this only by 
the fact that the tongue has a motion of its own, and 
can be by voluntary motion separated from the other 
parts of the mouth, so as to assure us that sapid sub- 
stances placed upon its surface and confined to its sur- 
face are instantly tasted. We thus get the same sort of 
evidence that the organ of taste is upon the fore part of 
the tongue, as that by which we learn that the organ of 
sound is in the ear, or the organ of smell in the nostril. 
The other parts of the mouth are not furnished with an 
apparatus of motion of their own, and therefore, in the 



52 SENSE-PERCEPTION. 

ordinary experience of the sensations of taste, we never 
learn whether the organ of the sense does or does not 
extend to certain other parts of the mouth. . This in- 
stance, therefore, instead of furnishing any objection to 
our general argument on this subject, is very strongly 
confirmatory of it. 

Like the sense of smell, this sense can render compar- 
atively little service in acquiring a knowledge of the 
material universe. It is confined to its own special class 
of ideas, and cannot be educated into any discernment 
of size, form, distance or direction. In its own sphere, 
however, it is almost preeminent among the senses in 
the variety, accuracy and delicacy of its discriminations. 

§ 38. This examination of the special senses which we 
have now completed justifies us in enunciating two pro- 
positions which are of great importance to the right 
understanding of our subject. 

I. All sensation is purely subjective, and becomes 
objective only by the aid of the muscular sensibility, 
the activity of voluntary motion and the experience of 
resistance to it from objects external to ourselves. 

II. There is no direct and immediate sense-perception. 
It is always indirect and mediate.* 

§ 39. Before closing this chapter it is desirable more 
fully to illustrate what has already been alluded to, that 
the special sensations have two functions, which may be 
distinguished from each other as the critical and emo- 
tional. The critical function of sensation is that by 
which it enables the mind to acquire a knowledge of 
material things around us. It is by this function of sen- 
sation that it becomes a factor in sense-perception. To 
this function almost exclusive attention has been given 
thus far in this Treatise. 

* Porter's Elements. Sec. 109. 



SENSE-PERCEPTION. 53 

The emotional function of sensation is that by which 
it furnishes peculiar sources of delectation, enjoyment, 
happiness, over and above the essential aid which it ren- 
ders to the mind in acquiring a knowledge of the mate- 
rial world. This distinction has hardly been as clearly 
marked by writers on the subject as it deserves to be. 
It is however obvious that it is real, and deserves to be 
fully recognized. For example, the sensation of taste 
has confessedly a very important function in enabling 
the mind to judge of the quality of the substances in- 
troduced into the mouth, with reference to their fitness 
for the nutrition of the body. But that sense has cer- 
tainly another function which is no less real and import- 
ant. It is to connect with the taking of food a unique 
and intense pleasure which can be derived from no other 
source, and without which it is improbable that men 
would provide and take a sufficient supply of various 
and nutritious food, to nourish the body and bring it to 
its greatest perfection. This pleasure added to the tak- 
ing of food greatly increases the happiness of life. 

The emotional function also requires a subdivision 
into the sensual and the esthetic. Of these the former 
is common to man and the lower orders of creation. 
The grazing ox evidently enjoys in a high degree the 
pleasure of taking and masticating his food. But the 
ox has no eye for the beauties of form and color, or for 
the harmony of sweet sounds. As has been already re- 
marked, the sensual function seems to be lacking in the 
senses of sight and hearing, while the esthetic seems for 
the most part to be confined to those senses, though 
some may be disposed to regard the art of cookery, and 
of the compounding of odors as being truly esthetic. 
Whether or not they are entitled to that rank is a ques- 
tion of small importance ; it is plain that they can bear 



54 SENSE-PERCEPTION. 

no comparison with those arts which are addressed to 
the eye and ear, as instruments of the culture and eleva- 
tion of the human soul. The object of those arts which 
are addressed to the senses of taste and smell is always 
sensual not intellectual. 

§ 40. Apparently, the sensual function was connected 
with the senses of smell and taste (and to speak the 
whole truth sex should be added), to secure the preser- 
vation and perfection of the animals and species of ani- 
mals in which it is found. It is however undeniable 
that it does immensely increase the happiness of all sen- 
tient beings. In many of the lower animals it appears 
to be true, that the senses of taste and smell are much 
more acute than in man, and very much more important 
to them in guiding their lives. Guided only by these 
senses, a large portion of the animal kingdom select their 
food with unerring accuracy, and that from the very 
moment of birth, without any of that uncertain expe- 
rience by which man learns to distinguish food from 
poison. Seemingly by the sense of smell alone, the dog 
tracks the footsteps of his master among the footsteps 
of a multitude of other men ; though we have no posi- 
tive proof that this is accomplished by the sense of 
smell. The dog may have some other sense of which 
we have no more knowledge than a race of deaf mutes 
would have of the sense of hearing. 

In the lower orders of creation these senses are an 
almost infallible guide to the attainment of the highest 
perfection of which the several species are capable. In 
man however it is far otherwise. He has a rational and 
moral nature of which all the senses are but servants, 
and must be in absolute subjection, or the most disas- 
trous consequences will follow. No greater ruin can 
come to a human being than that which results from the 



SENSE-PERCEPTION. 55 

indulgence of the lower senses uncontrolled by the intel- 
lectual and moral nature. 

§ 41. From the point of vision to which we have now 
attained, it is easy to see, how widely the rational nature 
of man separates him from all the irrational creatures 
that surround him, and to which in some respects he 
seems nearly akin. The brute has apparently the same 
senses as man, and some of them even in greater per- 
fection. But the relation of man's life to the senses is 
removed from that of the brute to the greatest possible 
distance. The brute has sensations, but no perceptions. 
In some way of which we have certainly little experi- 
ence, his sensations guide him directly to his destiny, 
without any of the slow processes by which man learns 
to mature sensation into rational perception. As the 
sensations of taste and smell guide him with unerring 
accuracy in the choice of his food, so the sensations of 
sight and hearing guide him with equal accuracy, in all 
those activities in respect to which it is necessary he 
should be guided by them. The use which he makes of 
his senses as the guide of his life is not the result of 
thought, nor of intelligence instructed by experience. 

It may be said in reply to this, that the inability of 
the infant to use his senses and his limbs at birth is the 
result of the physical weakness in which he was born. 
We reply that this is obviously not entirely the fact. 
Many persons have been born blind, and have acquired 
the power of vision in mature life. These persons do 
not, the moment the power of vision is acquired, spring 
at once into the full use of that sense after the manner 
of brutes, but must acquire the use of it by experience 
and the exercise of rationality in the very way already 
described. It is an intellectual process, just as truly 
and of the same character as the efforts of the philos- 



56 SENSE-PERCEPTION. 

opher to study nature in any department. We call the 
use which man makes of his senses sense-perception. It 
is a truly intellectual process from the beginning. We 
call the use which the brute makes of his senses instinct. 
We know little of the nature of the thino- we thus name, 
because we have little experience of that mode of guid- 
ing life ; yet we are not entirely without experience of 
it. The moment the hungry infant feels the source from 
which his nutriment is to be derived, between his lips, 
all the muscles concerned in the operation of sucking 
spring at once into cooperative activity, and the little 
being that otherwise must soon have died of starvation 
is nourished and reared up to manhood. There is no 
human intelligence in this, it is necessary activity ex- 
cited by instinct. So much we know by experience, 
though by an experience long ago forgotten. When 
therefore we ascribe brute activity to instinct, we do 
not use a word without a meaning. It has meaning in 
the history of our own lives. It is probable that this 
brute activity is produced by a method nearly analogous 
to that by which the chest of the new-born infant con- 
tracts and expands at the touch of air, or the pupil of 
the eye at the touch of light. 

The way in which brute life is guided is one and sim- 
ple. It is not the way of intelligent sense-perception, 
but the way of unintelligent sensation. His sensations 
simply stimulate and guide his activity to the attain- 
ment of his destiny. All the sensations of the brute 
direct him invariably and inevitably to a sensual life. 
He can live no other. To man the senses are the instru- 
ments which stimulate him to so much of sensuality as 
is needful for him, and guide his rational powers to that 
knowledge which is essential to a human life and to such 
culture as rational powers require to their full develop- 



SENSE-PERCEPTION. 57 

ment. Man therefore requires the three functions of 
sensation — the critical, the sensual and the esthetic — 
while the brute requires and is capable of the sensual 
only. Any account of the origin of man which does not 
recognize this broad distinction between human and 
brute life cannot be true. 

§ 42. At this point we can hardly forbear remarking 
that instinct, as thus explained, seems to be the point at 
which animal and vegetable life touch each other. A 
plant growing in a dark place to which a scanty supply 
of light only is admitted at a single opening, not only 
inclines from its natural perpendicular position towards 
the source from which the light comes, but greatly 
stretches itself beyond its normal length, as if in an 
effort to reach, if possible, a sufficient supply of light. 
This is very analogous to the manner in which instincts 
stimulate the activities of the brute. There are other 
cases in which the analogy is still stronger. The bee 
builds his cell on strictly geometrical principles, though 
he knows nothing of geometry and experiences no pleas- 
ure from an appreciation of the perfection of his work. 
In the same manner every plant in the garden, every 
weed by the roadside, every tree of the forest puts 
forth leaves and flowers, and seed vessels and seeds of 
the same form and color and texture and structure, with 
no intelligence and no appreciation of the perfection and 
beauty of what it produces. Man is guided by intelli- 
gence, and feeling, controlled by intelligence; the brute 
by an impulse of feeling without intelligence, and the 
plant by an impulse without either intelligence or feel- 
ing. 

§ 43. At the foundation of the esthetic function of 
sensation, lies the ultimate fact, that there is in the 
human soul a natural capability of discerning in the uni- 
10 



58 SENSE-PERCEPTION. 

verse that mysterious, undefined and undefinable quality 
which we call beauty. It is undefinable just as color is 
undefinable. It can be known only by experience. It 
is present in the innumerable forms and colors, and com- 
binations of form and color which are addressed to the 
eye, and in the endless multitude and variety of sound 
and combinations of sound which are addressed to the 
ear. To discern this quality and to present it to the 
mind as one of the most fertile and elevating sources of 
human happiness is the esthetic function of sensation. 

This function involves in a high degree the action of 
the iutellect, and never reaches its maturity except in 
the most perfect development of which the intellect is 
capable. In its maturity it preeminently implies the 
comparison of one thing with another, and a discern- 
ment of the relations of one thing to another, and of the 
part to the whole, and of the whole to its parts. And 
yet its presence is often most decidedly manifested in 
very early infancy. Au infant not one year old has been 
known to break out in hearty laughter at the sight of a 
handsomely turned bed-post, to cease laughing as soon 
as its eye was turned away from it, and to give the same 
manifestation of pleasure when agaiu getting sight of it. 
Admiration of the beautiful is certainly among the 
earliest manifestations of an intelligent nature which 
are seen in childhood. 

This may truly be termed sense-perception. As soon 
as the infant recognizes the forms and colors and sounds 
of external nature he also perceives beauty as one of its 
qualities just as he perceives its color or its form. It is 
not possible, however, to present the subject entire in 
this treatise because it implies more than sense-percep- 
tion — it involves the consideration of the higher thought- 
powers of the soul. 



SENSE-PERCEPTION. 59 



CHAPTER VIII 



Cooperation of the Senses. 

§ 44. Many writers have insisted strongly on the dis- 
tinction of original and acquired perceptions.* It will 
readily be perceived that, consistently with the views 
thus far advocated in this treatise, this distinction can- 
not be admitted as having any foundation in the phe- 
nomena we are dealing with. In whatever sense any 
one perception is original all perceptions are original; 
and in whatever sense any perception is acquired, all 
are acquired. It may be said that there are perceptions 
furnished by one sense alone, and others which cannot 
be acquired without the aid of more than one sense. 
Even this, however, can hardly be admitted. The eye 
can be trained to discern extension and judge of dis- 
tance ; but this is not accomplished by calling in the aid 
of another sense, but by the help of the muscular sensi- 
bility, voluntary motion and the experience of resist- 
ance from without. Even if we admit touch to a place 
among the special senses, the eye is not dependent upon 
it for the formation of its judgments of extension and 
distance. It is not true, as often asserted, that we edu- 
cate the eye to do the work of the sense of touch, and of 
touch to do the work of the eye. Both the sense of 
sight and touch (admitting touch to be a sense), inde- 
pendently of each other, derive their judgments of exten- 
sion and distance from the same sources. 

The real question in hand relates to the propriety of 
the distinction expressed by the words " original " and 

* Reid's Collected Writings, p. 184 ; Porter's Elements, Section 103 
and onwards. 



60 SENSE-PERCEPTION. 

" acquired." Whether the mind is dependent on a sin- 
gle sense or more than one is requisite, in either case 
the perception is not immediate knowledge, following 
directly on the sensation without any intervening pro- 
cess ; but mediate knowledge acquired by the interven- 
tion of a rational soul to interpret the sensation, and in 
interpreting it, the mind uses assistance derived from 
other sources than the sensation itself. It employs the 
aid, not of some other sense, but of the muscular sensi- 
bility in connection with voluntary motion. It is thus 
mediate and acquired, and not immediate knowledge. 
All perception then is acquired, not original. Neither 
the touch though admitted to a place among the special 
senses can discern an extended surface, nor the sight, 
the colored surface, without the aid of muscular sensi- 
bility. 

§ 45. There is, therefore, much less dependence of the 
senses on each other than is apt to be supposed. It is 
rather true that all the senses are dependent on knowl- 
edge previously acquired from the same sources than 
that one sense is dependent on another. The power of 
perception is not confined to one or two senses, as some 
authors of the highest respectability have maintained,* 
but is common to all the senses, and all the senses are 
alike dependent on the muscular sensibility and the act 
of voluntary motion for translating their sensations into 
perceptions. There are, however, certain respects in 
which there is a necessary cooperation of the senses with 
each other. For example, the soul must learn to identify 
the object as presented to one sense with that same ob- 
ject as presented to another. When one blind from 
birth has acquired sight at maturity, he has a good deal 
of difficulty in identifying the object which he has before 
* Porter's Elements, Sec. 88. 



SENSE-PERCEPTION. 61 

known by handling it, with that which he has now 
learned to cognize by vision. He may, for example, 
know the cat and dog by handling them, perfectly well, 
and he may easily distinguish them as visual objects, 
after he has acquired the power of vision ; but he must 
also learn to identify each as felt with the same as seen. 
He must learn to know how an object which affects the 
hand so and so when handled, will affect the sense of 
sight. He must become able to feel with his eyes and 
see with his hands. This is called an acquired percep- 
tion ; yet it is acquired in no other sense than any other 
perception. Both are equally the results of an experi- 
mental process. It is, however, a true cooperation of 
the senses of sight and touch (if we admit touch to be a 
sense), if we do not admit it to be a sense, it is coopera- 
tion of the sight with the feeling of contact. It is pre- 
cisely like the process by which the mind acquires the 
power of distinguishing by vision the plane surface from 
one which is curved or angular. 

§ 46. All the perceptions of sound involve this same 
cooperation. According to the definition of an original 
as distinguished from an acquired perception, there are 
no original perceptions of sound. All are acquired per- 
ceptions. They require the aid of the muscular sensi- 
bility in determining the direction from which the sound 
proceeds, and either of the eye and of the feeling of con- 
tact or the experience of external resistance in identify- 
ing the sounding body. The same thing is equally true 
of the sensations of taste and smell. We are thus 
brought back again to our position that no one sense is 
of itself adequate to any perception. Every possible 
case of sense-perception is a case of cooperation either of 
one sense with another, or of a sense with some form of 
muscular sensibility. 
11 



62 SENSE-PERCEPTION. 

By the cooperation of the sense of sight and hearing 
with each other and with the various forms of muscular 
sensibility, all the beautiful and eminently important 
results of oral and written language are produced. The 
organs of the human voice have a capability of all that 
variety of sounds, simple and combined, which consti- 
tutes spoken language, and by the aid of the muscular 
sensibility acquire the power of uttering these sounds 
at pleasure, under the control of the judgment and the 
will. Different minds are capable of agreeing to use 
certain sounds and combinations of sound as expressions 
of knowledge, thought and feeling. The ear is capable 
by its delicate organization of repeating those vibrations 
which originated in the voice, and by their being so 
repeated upon the acoustic nerve, the mind takes cogniz- 
ance of them, and thus the meaning of one soul is con- 
veyed to another with almost the rapidity of thought 
itself. 

The mind is also able to devise for each of these vocal 
expressions of the soul's meaning, signs addressed to the 
eye, by which they may be recorded to endure for ages, 
and be transmitted to any distance, and by the inven- 
tions of this age with the rapidity of lightning. Thus 
by the cooperation of the eye and the ear the meaning 
of one mind may be transmitted to any number of other 
minds, at any desired distance either of time or space. 
All this the human soul accomplishes by the intelligent 
and rational use of the senses. 

§ 47. Or, if the sense of hearing is lacking, signs ad- 
dressed to the eye may be substituted, instead of vocal 
sounds as representatives of thought. When, however, 
the effort is made to reduce this language of signs ad- 
dressed to the eye to a written language, great difficul- 
ties are encountered. In the case of an oral language 



SENSE-PERCEPTION. 63 

this is accomplished with comparative ease, because the 
number of elementary sounds necessary to the formation 
of a spoken language of the greatest copiousness is very 
small, not much exceeding forty. For each of these a 
visible representative is very easily invented and agreed 
on, and all other visible representatives of vocal signs 
are mere combinations of these few elementary sounds- 
Thus only twenty-six characters suffice to write all the 
fifty thousand words of the English language. It is 
difficult to conceive how a few elementary signs can 
ever be invented out of which in like manner all the 
visible signs necessary to the completeness of the sign 
language could be compounded. The cooperation of 
the eye and the ear would seem to be a necessary condi- 
tion of the construction of a written language which 
should be in the highest degree comprehensive and ex- 
pressive, and yet easy of acquisition. The difficulties 
encountered in the acquisition and use of the language 
of the Chinese well illustrate the principle. If the sign 
language were reduced to writing, it must be by the use 
of visible signs for things and not for souuds. The 
written language w T hich the deaf mute acquires in our 
present modes of teaching, is not the sign language 
reduced to writing, but our own written language as it 
presents itself to the deaf mute's eye, unaided by the 
sense of hearing from which we obtain it. It is an 
exceedingly difficult acquisition. If the human race had 
all been deaf mutes, their written language, if any at all 
existed, would have been exceedingly limited and inade- 
quate. It seems hardly probable that a race of deaf 
mutes could ever have brought the sign language to its 
present degree of perfection. 

§ 48. It is a conceded law of language that all terms 
expressive of mental acts and states are derived from 



64 SENSE-PERCEPTION. 

the various processes of sense-perception. It is only an 
application of the principle that all language is of ma- 
terial origin. It is a question of some interest from 
which of these processes such terms are chiefly derived. 
It is held by some writers* that they are derived chiefly 
from the sense of touch, or as we have preferred to call 
it, from a feeling of contact. This opinion can hardly be 
sustained. Perhaps it would be nearer the truth to say, 
that none of them can be said with any propriety to 
come from that source. On the other hand, they are 
mostly derived from the action of the muscles. We are 
said to take or apprehend one's meaning, certainly we 
do not take or apprehend a thing by touching it. We 
are said to hold an opinion, to comprehend or grasp a 
train of thought, to accept a proposition or a system. 
Not one of these forms of expression has any reference 
to touch, but all are derived purely from muscular ac- 
tion. Even that word, which by the common consent 
of all the philosophers of all schools, is used to express 
the action of the mind in acquiring a knowledge of the 
material world, perception, is derived from the Latin 
capio to take, thus suggesting in all its uses that original 
source of all our knowledge of the material universe, 
muscular action. Thus the very phrase sense-perception 
implies and suggests the truth of the doctrine which has 
been advocated in this treatise. 

§ 49. Music is also dependent on the cooperation of 
the senses. The existence of music is quite independent 
of the sense of sight, but it is certainly dependent on 
the muscular sensibility. All music depends fundamen- 
tally on the varieties of pitch which the human voice is 
able to utter, and the human ear to distinguish. But 
such control of the element of pitch as is necessary to 

* Porter's Elements, Sec. 99. 



SENSE-PERCEPTION. G5 

the simplest melody is attainable only through the ex- 
perience of the muscular sensibilities which attend the 
modulation of the voice, or the movement of the fingers 
in playing the instrument. Experience of the same 
muscular sensibility is equally necessary to harmony, 
and to the rhythm of music. The production of written 
music is dependent on the cooperation of the eye and 
the ear in precisely the same way as written language ; 
since in music the number of elementary sounds is very 
few, out of which all others are compounded. It is only 
necessary to express each of these elementary sounds 
by a sign addressed to the eye and the problem is solved. 

We have seen that if the sense of hearing were want- 
ing, language would still be possible through the eye ; 
but that this could become a written language only to a 
very limited extent. The same difficulty would not how- 
ever exist in the -way of written music, if the sense of 
sight were lacking. The mind could devise expressions 
for the elementary sounds of all music which should be 
addressed to the feeling of contact and the muscular sen- 
sibility, and with these the blind could read music, just 
as they now read the page which is printed with raised 
letters. Neither would the blind have any special diffi- 
culty in reducing a spoken language to writing, if they 
could devise means of printing in raised letters without 
eyesight. If all men were blind, the necessity would 
be imperative of printing all books and all music in 
raised characters, or at least in some form which could 
be read by contact and motion. It is not however prob- 
able, that without the sense of sight the race could ever 
have attained to sufficient prosperity or civilization, to 
have used either written language or music. 

§ 50. All the higher forms of beauty require the co- 
operation of the senses. There is a degree of beauty 



66 SENSE-PERCEPTION. 

in a single bright color, and a higher degree of it in 
skillful combinations of color ; but a still higher degree 
of it is always attainable by combinations of beauty of 
color with beauty of form. These combinations of 
course can only be produced by the cooperation of all 
those powers by which we acquire the ideas of color 
and form. So in music the highest beauty requires the 
most skillful combination of pleasing sounds and sounds 
expressive of emotion with pleasing movement. 

The highest esthetic effects can only be produced, 
when art successfully imitates nature. This is the great- 
est triumph of genius. We have seen that the mind is 
made acquainted with material objects by a picture 
formed on the retina of the eye. Imitative art employs 
just such a combination of light and shade painted on a 
plain surface, as the lenses of the eye paint on the optic 
nerve, to represent the object to the mind, and to all 
minds alike. The perfection of the painter's art lies in 
conceiving by the imagination precisely the combination 
of light and shade which any object or group of objects 
placed before the lenses of the eye would paint on the 
retina, and in the skill perfectly to imitate that combi- 
nation on the canvas. Each perfect eye will then trans- 
fer that representation to its retina, and thus each be- 
holder will see reproduced the object which the painter 
meant to represent. He not only perceives the colors of 
the object, but its form and proportions, not only how it 
would look but how it would feel. The objects so rep- 
resented may be anything which the eye cau perceive, a 
tree, a flower, an animal, a landscape, or the human face 
divine. In this latter case it would represent to the 
mind a great deal more than form and color, a great 
deal more than mere physical qualities, it would repre- 
sent thought, feeling, purpose, character. Thus the 



SENSE-PERCEPTION. 67 

whole power of the most skillful painter lies in correctly 
conceiving and representing on the canvas, that combi- 
nation of light and shade which the lenses of the eye 
would paint on the retina. Of course this implies that 
power of the imagination which conceives of a subject 
worthy in the highest degree to be so represented. 



CHAPTER IX. 



The Activity of the Soul in Sense-Perception, 
and the Products which it Evolves. 

§51. If the views of Sense-Perception insisted on in 
this treatise are sound, there is no occasion to raise the 
question whether the soul is active or passive in that 
experience. We have traced its activity at every step. 
We have seen that it commences its career of acquisi- 
tion in utter ignorance of the universe outside of itself, 
and that it makes its way out of that prison of darkness 
and confinement by putting forth its own activity, just 
as truly as the young oviparous animal makes its way 
out of the darkness and confinement of its shell into the 
light and freedom of the world without by breaking its 
own shell. Its first achievement is to acquire the power 
of motion under the control of the will. Till this is 
learned nothing of the external world can be known. 
No sooner, however, has the soul made this acquisition 
than it finds that power which it consciously exerts 
hindered from going out into result by some resistance. 
By an intuition of which we can give no account, other 



68 SENSE-PERCEPTION. 

than that it is of the nature of the human soul, as soon 
as it becomes conscious of being itself a cause, to look 
for a cause for whatever happens, the mind sees in this 
resistance a resisting cause which is not the acting ego. 
It is known that the resistance is a non-ego, for the cau- 
sative power which the ego consciously exerts is hind- 
ered from going into effect. The condition of his 
experiencing that resistance is the exertion of his own 
active power. Thus, the first hint a human soul can 
ever get of the existence of the non-ego is conditioned 
by its own conscious activity. 

His second step in the process is in like manner de- 
pendent on his conscious exertion of the same power of 
voluntary motion. As soon as he experiences and rec- 
ognizes resistance, he finds that that resistance hinders 
voluntary motion only in a certain direction, while in 
all other directions it is free. He also finds by trial 
that that resistance only exists within certain limits, and 
by successive trials he ascertains the limits within 
which the resistance is experienced. Moving his hand 
backwards and forwards he finds that within these 
limits resistance is continuous ; beyond them motion is 
free. This reveals to him an extended surface or exten- 
sion in two dimensions. In like manner it has been 
shown how by the same exertion of his power of volun- 
tary motion he is conducted to a knowledge of the third 
dimension of extension, of solidity, of form, and in gen- 
eral of external bodies. For all these acquisitions he 
has been dependent on exerting his power of voluntary 
motion and his experience of resistance to that power 
when exerted. 

§ 52. This, however, is not the whole truth. This 
necessity for the activity of the soul not only pertains 
to the first acquisition of the power so to use the senses 






SENSE-PERCEPTION. 69 

as to acquire the knowledge which they are able to fur- 
nish, but it pertains to all the experiences of sense-per- 
ception throughout life. Innumerable cases which occur 
in the experience of every man prove that it is quite 
possible that a sensation many be experienced through 
the proper organ of sense, and yet without an act of 
attention, there will be no perception. A man can per- 
ceive nothing with any of the senses when the attention 
is wholly absorbed in another direction. One's atten- 
tion may be so entirely fixed on a mathematical problem, 
that a friend may enter his room, and even speak his 
name without being perceived either by the eye or by 
the ear. Two persons may have been born and reared 
in the same house and amid the same natural surround- 
ings, and yet one of them will know a multitude of 
things about the environment of that home of which the 
other remains entirely ignorant. Their senses may be 
equally acute and yet one of them fails to know much 
which the other learns from childhood. The only reason 
is that the one gives his active attention to the objects 
around him, while the other fails to do so. All sense- 
perception is thus seen to depend on the mind's activity. 
No matter how keen the senses may be, we perceive 
what we attend to and that which we do not attend to 
we do not perceive. No sensation can ripen into per- 
ception without the interpretation of an active ration- 
ality. It is like the frequent experience of the mind in 
reading a book. The eye may pass along the page and 
see every letter, and yet the activity of the mind to 
invest those letters with their proper meaning is not ex- 
erted, and therefore the man finds that he knows noth- 
ing of the subject matter of that which has passed 
before his eyes. Some men can read in the midst of 
conversation and understand what they read, because 

12 



70 SENSE-PERCEPTION. 

they fix their attention on the book and do not hear the 
conversation. Another hears the conversation and 
therefore understands nothing of what he reads. The 
mind actively chooses to which it will attend. 

Of two men who take a journey together, one returns 
with a mind stored with a knowledge of innumerable 
objects of interest of which the other has learned noth- 
ing at all. To one mind the universe, nature, society, 
history — all things are full of lessons of wisdom. To 
another mind enjoying the same advantages the whole 
scene around him is a blank, imparting no instruction 
and no wisdom. One of these minds is active, the other 
without activity, putting forth no energy beyond what 
is necessary for the physical uses of each hour as it 
passes. The mind exercises the power of selection 
among the objects presented to the senses, giving atten- 
tion to those things which it regards as important to be 
known, and drawing attention away from those things 
which it regards as unimportant. We thus select our 
own food by our own mental activity, just as the brute 
selects its physical nutriment by the acuteness of sensa- 
tion. 

§ 53. If the views maintained in this treatise are true, 
we must regard the activity of the mind in sense-percep- 
tion as of a very high order. The problems which the 
infant mind solves in the first three years of its life may 
well excite our wonder and admiration. During this 
period he not only learns to interpret the indications of 
his senses, in all the multiplied forms in which sensations 
must be translated into perceptions, but during the same 
period he learns at least one oral language. All this is 
accomplished by the spontaneous activity of the mind, 
without the intervention of any teacher. The results of 
this spontaneous activity should inspire our reverence 



SENSE-PERCEPTION. 71 

for the human soul even in its early infancy. Are we 
not often too much in haste to interrupt this process of 
spontaneous development by what it may be feared is 
the impertinent intrusion of direct teaching? Do we 
not undervalue the results which this spontaneous devel- 
opment ought to produce and would produce, if not 
interfered with, in years subsequent to the time when 
we insist that the process of school education must be 
commenced ? We here touch a topic which is worthy 
of more thought than has yet been bestowed upon it. 

§ 54. Our admiration of infant activity will be raised 
to a still higher point, if we bear in mind that in the 
solution of these problems of sense-perceptions, the 
infant must in greater or less degree bring into exercise 
all his higher mental faculties. His memory must be 
almost constantly active. It is commonly said, and in a 
certain sense truly, that sense-perception comes before 
memory; yet the mind can make no progress in sense- 
perception without the help of memory. It advances 
step by step by a series of experiments, and in order 
that it may derive any benefit from these experiments, 
it must be able to recall them whenever a similar case 
arises. 

Even the infant must practice inductive reasoning. 
When by experiment he has found that in a given case a 
certain combination of light and shade indicated the 
presence of a curved surface, he must infer that this 
combination always indicates the same thing. He must 
have and rely upon the intuition of the uniformity of 
the course of nature. As we have already seen, the 
intuition of cause and of substance as revealed by attri- 
butes must be always at his command. Not that he 
formulates these iu tuitions, and expresses them as gen- 
eral propositions, but he relies upon them, assumes and 



72 SENSE-PERCEPTION. 

applies them. Without them there can be no activity of 
a rational soul, no progress in knowledge. It is true that 
the chief activity of childhood is in the sense-perceptions ; 
but this activity always implies in greater or less degree 
all the powers of the intellect. Even an infant in its 
mother's arms is in a greater or less degree an inductive 
philosopher. There is no foundation whatever for Her- 
bert Spencer's assertion, that the " primitive man " has 
no idea of cause and knows nothing of any course of 
nature. No man, however " primitive," acquires the 
notion of cause or learns the uniformity of the course of 
nature by induction ; but must know both by a natural 
intuition, as a condition of his learning anything else. 
A wise man will reverence infancy. It finds its way out 
of ignorance into knowledge, not by receiving knowledge 
passively, but by acquiring it by personal activity. 

§ 55. The product of this activity of the soul is a con- 
ception or notion of the object as an individual thing, 
which can be recalled and used at pleasure. That con- 
ception is made up of all the qualities or individual per- 
cepts which have been found to belong to the object. 
It is an interesting question, by what constructive law 
this complex product is formed. In order to explain 
this matter clearly, it is necessary to define a term which 
we have not hitherto had occasion to use. 

A percept is the mind's knowledge of a single quality, 
attribute or causal power of an object. Thus the culor 
of an object is the percept of it which is gained through 
the eye. On the other hand, the perception of an object 
is the notion of it gained by the use of all the powers 
which the mind uses in the process of sense-perception, 
united in one complex whole. 

Some maintain that this completed product is first 
formed by uniting the several percepts under the rela- 



SENSE-PERCEPTION. IS 

tions of time and space ; that in the first experience of 
infancy they are united by no other bond than the fact 
of their having been experienced at the same time and 
in the same place. Consistently with the principles thus 
far advocated, we cannot accept this view. In every 
product of sense-perception, the constructive law is that 
of the intuition of cause, and of the relation of substance 
and attribute, the concurrence of the two percepts in 
time and place being only important as suggesting the 
notions of cause and quality. 

We have already seen that the first step made by the 
mind in acquiring a knowledge of any thing external is 
the recognition of a resisting cause. We have no knowl- 
edge of any external object except at least by one of its 
causal relations. We are dependent on the same recog- 
nition in taking that second step by which we gain a 
notion of a surface extended in length and breadth. It 
is accomplished by noticing the continuity of resistance 
within a given outline. This assumes that the surface 
has everywhere the causal power of resistance. In the 
same manner the boundaries of that surface may be 
traced by noticing its causal power to produce certain 
sensations of color. So of all the other percepts. By an 
inevitable necessity, we form the complex notion of the 
object by recognizing its causal powers. At the same 
time we recognize the object as a being or substance 
manifested to us by these causal powers. 

The intuition of causal power and of the relation of 
substance and attributes is thus interwoven with every 
act of sense-perception. We do, however, learn that 
each particular impression on the sensibilities is the 
product of the causal power of the resisting non-ego, 
by the fact that we experience that impression simulta- 
neously with our experience of the resistance. 
13 



74 SENSE-PERCEPTION. 

§56. It is a question of considerable interest, whether 
in forming such a complex notion of any individual 
object, the mind embraces at a single view many or all 
of the percepts which enter into it, or is by its nature 
confined at each moment of time to a single percept, and 
unites them into one whole by passing from one to 
another with so much rapidity as to seem to itself to 
contemplate them all at the same instant. The latter of 
these views, which is defended by Dugald Stewart and 
some other writers,* assumes that the human mind is 
incapable of attending to more than one object at the 
same moment, and can therefore join many objects into 
one whole only by such rapid transition from one thing 
to another. For example, when we are listening to an 
orchestra consisting of many instruments, we do not, as 
we are apt to suppose, attend to the whole performance 
at once, and thus experience the effect of the whole, but 
to each instrument in its turn, passing from one to 
another with such rapidity that the impression of the 
whole seems to be received at the same instant. 

From this view of the subject, President Porter dis- 
sents, as it seems to us with the best of reasons. The 
assumption that the human mind can attend to but one 
thing at the same moment, seems to rest on no substan- 
tial foundation. If that doctrine is true, it is inconceiv- 
able that the mind should be able to compare one thing 
with another. The act of comparison necessarily implies 
that both objects are present to the view at the same 
time ; if not, how is it possible that any judgment should 
be formed of the relations of the two to each other? If 
I pass instantaneously from intense illumination to total 
darkness, how is it possible that I should feel the con- 

* Porter's Elements, Sec. 120, referring to Dugald Stewart's Ele- 
ments, Ch. II. 



SENSE-PERCEPTION. 15 

trast, unless ray mind contemplates both the darkness 
and the light at the same moment ? If to this it is re- 
plied that the mind contemplates at the same moment, 
one of these objects as present and the other as remem- 
bered, this does not in the least relieve the difficulty. 
We can as easily admit that the mind attends to two 
objects at once, as that it attends to one object and the 
remembrance of another. One or the other of these sup- 
positions must be admitted to be true, or the comparison 
of one thing with another must be forever impossible to 
the mind. The denial that the mind can attend to more 
than one thing at once is a virtual denial of the power of 
comparison. 

It may be and probably is true that when the mind 
attends to more than one thing at once, it does not 
attend to all with equal intensity, that it does give chief 
attention first to one and then to another, and that these 
transitions are made with very great rapidity ; but it 
remains none the less true, that when two or more things 
are compared they must all be present to the mind and 
receive a greater or less degree of attention at the same 
moment. In listening to a musical performance, it is 
doubtless true that many if not most persons can, if they 
choose, single out some one instrument and follow it 
with exclusive attention through the whole performance ; 
but if one does so he will lose entirely the effect of the 
harmony of the whole. If that is to be appreciated, the 
mind must attend to all the instruments at once. In 
like manner all the percepts which make up the complex 
notion of any individual thing must be jointly contem- 
plated by the mind at the same moment. 

§ 57. By these activities of the soul in sense-percep- 
tion, we come at last to a knowledge of all the qualities 
of known material things. It is not by the senses alone, 



76 SENSE-PEECEPTION. 

nor even by the senses as aided by the muscular sensi- 
bilities. The memory, the reasoning powers and the in- 
tuitions must all bear an essential part in these processes. 
But the soul can come to a knowledge of none of the 
qualities of matter without applying to them the pro- 
cesses of sense-perception. Before we dismiss the sub- 
ject it is desirable to take a more comprehensive view of 
these qualities, and to form a classification of them ac- 
cording to their relations to the powers and methods 
by which a knowledge of them is acquired. It has been 
usual with writers on Psychology to divide the qualities 
of material bodies into two classes ; the primary and the 
secondary.* The former class embraced all those qual- 
ities which are inseparable from our notion of a material 
body. They are such as extension, space-filling power 
or impenetrability. The second comprehended the rela- 
tions of material bodies to each other and to the senses. 
Sir William Hamiltonf suggested three classes ; the pri- 
mary, the secundo-primary and the secondary. In the 
primary he embraced the space relations of matter ; in 
the secundo-primary, the relations of resistance, gravity 
and inertia, or in general the relation of bodies to one an- 
other ; and in the secondary the causal powers of matter 
to produce special sensations. At first view the classifi- 
cation of Sir William Hamilton seems to be accurate 
and exhaustive. 

The views however presented in this treatise, if just, 
enable us to define the three classes more accurately, 
by referring each of the classes to the powers through 
which, or more accurately the method by which the 
qualities embraced in it are cognized by the mind. The 
definitions would be as follows : 

* Reid's Collected Writings, pp. 845, 846. 

f Hamilton's Metaphysics, p. 334, Bowen's Edition. 



SENSE-PERCEPTION. 11 

The primary qualities are those of which we require a 
knowledge by voluntary motion. They are the space- 
relations of matter. 

The secundary-primary are those which we cognize 
by experienced resistance to voluntary motion. They 
are outness, gravity, inertia, hardness, roughness, and 
the like. They become known to us by the resistance 
which they offer to our voluntary motions. 

The secondary are those qualities which we cognize 
by sensations produced in our special senses. They are 
color, sound, taste and smell. 

In this definition of the classes externality or outness 
should be embraced in the secundo-primary as extension 
is in the primary. This quality is not embraced in 
either of the classes suggested by Sir William Hamil- 
ton. With this addition to the secundo-primary, it is 
believed the classification is strictly exhaustive, and 
that the definitions proposed above are accurate. Per- 
haps it may be regarded as no small confirmation of the 
views of sense-perception advocated in this treatise, that 
they conduct by a logical necessity to such a classifica- 
tion of all the qualities of matter, and furnish defini- 
tions of the classes so simple and comprehensive. 

Perhaps it would be wise to drop Sir William Hamil- 
ton's unmeaning and rather clumsy names for the three 
classes, and substitute in their stead a nomenclature 
derived directly from the definitions just given and 
suggestive of them. Let us call them, qualities cogni- 
zed through voluntary motion, qualities cognized through 
resistance experienced to voluntary motion, and qualities 
cognized through the special sensations. Thus the clas- 
sification of the qualities of matter will be a compend 
of the whole complex process of sense-perception. 



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